Enchanted Rock (Peter T. Flawn Series in Natural Resources)

The great Texas wind rush: Peter Warlock Novels 1: Peter Warlock Novels 2: Peter Wimsey Series Peter Wimsey Series Bk 1: Peterson Field Guide Series. Peterson Field Guide Series A field guide to insects: Borror and Richard E. White ; color and shaded drawings by Richard E. White ; line drawings by the authors. McKnight and Vera B. McKnight ; illustrations by Vera B. A field guide to freshwater fishes: Burr ; illustrations by Eugene C.

Peterson Field Guide Series 7: Pough, photographs by Jeffrey Scovil. Peterson Natural History Companions: Peterson Reference Guide Series: Not all the earthquakes in the Texas Panhandle are situated over the Amarillo-Wichita Uplift; several earthquakes have been reported in neighboring sedimentary basins. The largest of these, with magnitude 5. Similar earthquakes occur in northeastern New Mexico and southeastern Colorado along a trend that may well be a western extension of the AmarilloWichita system King ; Goldstein Presumably these earthquakes, like those in Borger and New Madrid, occurred on existing faults reactivated by present-day stresses.

On 15 February a magnitude 4. It is possible that the Perryton event was part of a trend of earthquakes that runs through the Anadarko Basin and includes the El Reno and the Durham earthquakes, both in Oklahoma Gordon Finally, regional seismograph stations recorded several small earthquakes with locations in eastern Oldham County. This region is sparsely populated, and we are unaware of any felt reports.

The largest of these earthquakes had a magnitude of only 3. Some petroleum is produced in this region, and thus these quakes may either be induced or of natural origin Davis The hazard from earthquakes occurring here is considerably lower than in West Texas or the Panhandle. However, the region is of special concern because of the concentrated population in the Dallas—Fort Worth area and because it faces potential hazard from several different kinds of earthquakes—naturally occurring earthquakes, earthquakes induced by human activity, and huge but relatively distant earthquakes that occur outside the borders of Texas.

The greatest hazard in this region is from very large, distant earthquakes. For example, the highest intensities for the — New Madrid earthquakes were at the Missouri-Tennessee boundary, where the earthquakes produced waterfalls on the Mississippi River and actually caused the river to change its course.

Although these intensities do not level ordinary buildings, they undoubtedly would produce widespread damage. There is legitimate reason to worry about how tall buildings, highway overpasses, and dams would respond to another magnitude 8 earthquake in the New Madrid region. It is possible that earthquakes in Oklahoma, such as the quakes of 22 October and 9 April , might affect northeast Texas. Felt areas of representative earthquakes affecting northeast Texas. Thick solid lines and plotted Roman numerals indicate estimated intensities for the 16 December New Madrid earthquake.

Information shown is revised from maps in Davis, Pennington, and Carlson Northeast Texas does experience small, natural earthquakes of its own. On 12 April an earthquake with magnitude 4. Inexplicably, Sellards called this the Trout Switch earthquake even though we have found no town named Trout Switch on maps from either then or today. Similarly, reservoirs are not responsible for a series of earthquakes that struck the Hemphill-Pineland area of eastern Texas between April and August Moreover, the highest intensities in the felt areas coincide with neither reservoir.

Thus these earthquakes are of natural origin. While a temporary seismograph station deployed in near Hemphill recorded more than seventy earthquakes with magnitudes as great as 4. In contrast, petroleum production probably did induce at least two earthquake sequences in this region. On 9 April , a magnitude 4. From intensity reports Sellards a concluded that the Mexia earthquake originated on one of the major faults of the Mexia system. While a natural origin for this event is possible, the coincidence of the earthquake location with the area of highest hydrocarbon production strongly suggests it was induced Sellards a; Yerkes and Castle ; Carlson Similarly, petroleum production is probably also responsible for a series of four earthquakes, the largest with magnitude 4.

By the time of the earthquakes, more than 3. Moreover, it seems unlikely that a quake with magnitude as great as 4. Its location has never been associated with any known fault. As in northeast Texas, these include quakes with both natural and human origins. However, the events are rare and quite small, so they probably pose little or no hazard. Both of these quakes had magnitudes of about 4. The quake was felt most strongly in southern Travis County, and because of the rarity of seismic activity, there was much consternation and some confusion about what had actually occurred.

The Austin Daily Statesman reported that: The San Antonio Express reported: The mysterious explosive noise and earth trembling which occurred on Thursday about noon and was heard and felt throughout a wide section of the country was explained today by M.

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Houston, a well known farmer living on Cedar Creek. He says the phenomena [sic] was caused by a meteor which exploded near Pilot Knob. When within a mile of them, the meteor burst and the concussion threw them to the ground. A search is now being made for fragments of the meteor. Felt areas of representative earthquakes affecting south-central Texas.

Information shown is revised from maps in Davis, Pennington, and Carlson , Davis, Nyffenegger, and Frohlich , and Bilich and others Neither of these earthquakes can be attributed to petroleum production, since oil was not discovered in this part of Texas until East of the Llano Uplift, the main tectonic features in central Texas are a series of fault systems that are part of the so-called Ouachita Belt, which extends from Mexico through central Texas to Oklahoma and Arkansas.

One such earthquake, with a magnitude of about 3. Although this earthquake was of natural origin, its precise cause is undetermined. This earthquake and similar small events that occasionally occur in southeast Texas and in Louisiana might be caused by movement within the salt domes found in several places near the surface. Within these domes the salt tends to move upward because it is less dense than surrounding sediments, and small earthquakes could occur when the accumulated strain within overlying sediment is released along faults.

Farther to the southwest, a number of Texas earthquakes almost certainly have been caused by petroleum production. After a 3 March Pleasanton quake scientists deployed several temporary seismographs, and analysis of the resulting data demonstrated that the events originated at or near the intersection of the fault contact Pennington and others The largest of these earthquakes, with a magnitude of 4.

The intensities in the epicentral region were MMI VI, which is high for such a small earthquake; this suggests that the focal depth must have been quite shallow. A notable feature of this earthquake was that it attracted the attention of the Branch Davidians, a religious group that was under siege at this time by the FBI near Waco, Texas.

United Press International reported on 12 April The Balcones Fault is the boundary between the central Texas hill country to the west of Austin and the flatter plains regions to the east. About 10 million years ago this was a very active fault, but it is quite inactive nowadays.

When slip is ongoing, the fault is active. After the slip stops, the fault remains. Thus in Texas and elsewhere the land is riddled with faults that no longer present any significant earthquake risk. There are numerous examples of faults that are active but that do not have any earthquakes. Land in some communities southeast of Houston, such as at Clear Lake and Dickinson, is sinking because water has been pumped from the ground for many years; this sinking may be associated with slip along faults. Photo by Tom Frohlich. In any particular region, the level of earthquake hazard depends on many factors.

These include the size, location, and frequency of earthquakes that might occur. The amount of damage they could cause also depends on the population density, the topography, the thickness and type of soil cover, and the nature of man-made improvements In practice, the most important factor affecting scientific hazard estimation is the historical record of earthquake activity; regions that have had large earthquakes in the past will certainly experience them again.

Although scientists who estimate hazard do include information about mapped faults, this information is less important than the historical record, since many known faults are not seismically active and since damaging earthquakes sometimes occur on unmapped, unknown faults. In the central United States, the USGS assesses the greatest hazard in the MissouriTennessee area, where three earthquakes with magnitudes of 8 or greater occurred in and Unfortunately, the very rarity of large earthquakes makes hazard analysis an inexact science.

In the twentieth century the largest earthquake in the Missouri-Tennessee area only had a magnitude of about 5. If the — quakes had occurred in New Madrid a few hundred years earlier, prior to settlement by literate peoples, would scientists know that such large and damaging earthquakes were possible there? Are we certain that earthquakes with magnitude of 7 or 8 have never and will never occur in Texas? No, we are not certain. Drilling itself does not cause earthquakes. However, earthquakes in some parts of Texas may be induced by the pumping of fluids at oil and gas fields or by the injection of fluids to dispose of chemical wastes.

The earthquakes in the Fashing-Pleasanton area southeast of San Antonio are almost certainly caused by or triggered by pumping; such earthquakes also occur near Snyder, Texas. However, most of these earthquakes are not dangerous because 36 they usually are very small—most are tiny and occur within a few tens of meters of the injection well Phillips and others In rare cases when injection induces larger earthquakes the magnitudes are seldom greater than about 4.

Moreover, while there are tens of thousands of oil and gas wells in the state of Texas, in only a few fields does evidence indicate that oil and gas pumping induces earthquakes. Until 24 March Texas had no known seismic activity south of the Fashing earthquakes; however, on that day a magnitude 3. Texas Earthquake Hazard How serious is the hazard in Texas from potential earthquakes? For Texans, it is important to remember three essential facts: First, earthquakes do occur in Texas.

People in two regions, West Texas and the Panhandle, should expect earthquakes with magnitudes of about 5. In northeastern Texas the greatest hazard is from very large earthquakes magnitude 7 or above that might occur outside of Texas, particularly in Missouri, Tennessee, or Oklahoma. In south-central Texas the hazard is generally low, but residents should be aware that small earthquakes could occur there, including some that are triggered by oil or gas production. Elsewhere in Texas, earthquakes are exceedingly rare.

Outside of the four geographic regions discussed above, earthquake hazard is as low as almost anywhere in the United States. The USGS estimates do not yet incorporate all the information presented in this book, and thus the maps underrepresent Texas earthquake hazard. Earthquake hazard map for the continental United States as prepared by the U. In many places such as Texas, the absence of detailed historical information means that earthquake hazard may be higher than indicated in this figure.

In most parts of Texas there is no need to enact sweeping changes in construction practices or take other drastic measures to mitigate earthquake hazard. From this, the most memorable fact many of us learned was that Alaska and Texas are the largest states, with Montana and California not too far behind; other states are not even close. In the past eighty years Alaska, the largest state, has experienced the largest earthquake of all, the 28 March Good Friday earthquake, with a magnitude Mw of 9.

The 18 August Hebgen Lake earthquake in Montana, with a magnitude of about 7. Since no other states have had earthquakes nearly as large as these, although, as we shall see, several had similarly large earthquakes earlier. The earthquake, for example, is the second largest earthquake we know about—anywhere. The water displaced by these uplifts produced a tsunami that was responsible for most of the damage and the majority of the fatalities. Although the most devastating effects of the tsunami were in Alaska, it also drowned 4 people camping on the beach in Depoe, Oregon, and 10 more people at Crescent City, California, where it also demolished stores and littered the streets with redwood logs from a nearby sawmill.

As remarkable as this earthquake was, it was not particularly unusual for Alaska. Locations of largest known earthquakes within each state in the continental United States, as reported in Stover and Coffman Symbols indicate event magnitude. Stover and Coffman As discussed in chapter 1, there are different magnitude scales, and for earthquakes occurring prior to about reported magnitudes are notoriously variable.

On 4 February another Aleutian quake, still farther to the west in the Rat Islands, had a magnitude Mw of 8. Indeed, the , , and quakes were so large that they were directly responsible for the invention of the moment magnitude, or Mw scale see chapter 1. Thus, the moment magnitude Mw was developed to properly measure the sizes of both large and small earthquakes. Nowadays, if both magnitude measures are available, most seismologists prefer to use Mw rather than MS to measure earthquake size. As discussed in chapter 1, there are different magnitude scales, and for earthquakes occurring prior to about , reported magnitudes are notoriously variable.

Since Alaska did not become a state until 3 January , a nitpicker could argue that for most of the twentieth century, California actually was the state with the largest earthquakes. While California may have lost its claim in , it certainly does experience large earthquakes; up to the present it has suffered more earthquake damage and more earthquake fatalities than any other state see table 3.

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In historic times two California earthquakes have had magnitudes of 8 and above. The better-known was the San Francisco earthquake of 18 April ; with an estimated 3, fatalities, it has been the deadliest earthquake to occur in the United States. In San Francisco was a major commercial center, and the quake leveled numerous buildings. Dunbar and others , updated with estimates of insured losses for more recent quakes; damage in dollars for year calculated using U. Bureau of Labor Statistics consumer price index for all urban consumers.

At Ventura the roof of the mission church collapsed. The quake caused only one fatality, when an adobe house fell. Because of the sparse population in the area in , this quake caused little damage. Were it to occur now, though, it would be the most destructive California earthquake since Europeans settled in California in the eighteenth century Wood ; Allen As noted in sidebar 2.

This certainly seems to be true in California. Considering the risk from earthquakes, is it safe to move to California? California can be safe, but as is true anywhere, you need to exercise some common sense about where you live and work. Before finding a home in California you might want to find out where the known active faults are and avoid living in poorly constructed stone buildings or in structures situated on steep slopes.

But is the pressure off? And even if a magnitude 8 does occur in California, it does not necessarily reduce the chances that another big quake could occur. For example, in — when the New Madrid earthquakes occurred, three shocks, each with a magnitude near 8, struck in a three-month period. If they do have a cycle, a big earthquake should reduce stress for some time. Light bulbs are a familiar example of a relaxation phenomenon. All bulbs burn out eventually, but new light bulbs are more likely to burn out than bulbs that have been used for a while.

Seismologists tend to group western Nevada in the same geologic province as California. Whether the judges of the Big-States Earthquake Contest would let this pass is unclear, but certainly Nevada has had some huge earthquakes. The largest, which occurred on 3 October and had a magnitude of 7. Nevada experienced two other earthquakes almost this big, in and The public heard little about the Nevada events, however, probably because no one was killed and the state was so sparsely populated.

Outside of Alaska, California, and western Nevada, the largest twentiethcentury U. This quake produced extensive surface faulting near Hebgen Lake, a manmade lake formed by damming the Madison River west of Yellowstone Park. It also caused a landslide that further dammed the river and created a second, natural lake now called Earthquake Lake downstream of Hebgen Dam.

If you are interested in earthquakes, the Hebgen Lake area is a wonderful place to visit. Parks Service operates a museum where the slide occurred. One of the authors of this book speculated that the damming of the Madison River might have been one factor that contributed to triggering the Hebgen Lake earthquake Frohlich If so, it would make it the largest earthquake known that was induced by a manmade lake or reservoir.

However, other scientists Zreda and Noller subsequently analyzed the effect of cosmic rays on bedrock along the fault scarp and concluded that the fault apparently had slipped six previous times over the past 24, years. A manmade origin for the earthquake now seems unlikely. To achieve the highest levels of hazard, a region must 1 be subject to large-magnitude earthquakes and 2 have a lot of people and buildings. By these criteria, Seattle and the surrounding region is the highest-hazard area in the United States, outside of California.

The largest, with magnitude 7. The 13 April Olympia earthquake had magnitude 7. A half-mile section of a meter cliff toppled into Puget Sound near Tacoma. The 29 April earthquake that occurred near Seattle was somewhat smaller, with a magnitude of 6. The 28 February earthquake had a magnitude of 6.

Although it produced at least a billion dollars of damage in Seattle, Tacoma, and surrounding areas, few lives were lost since the earthquake focus was unusually deep about 50 km and it did not occur beneath a heavily populated area. One side argues that the largest quakes will not have magnitudes larger than about 7. Just think about how devastating such an earthquake would be if it occurred nowadays, considering that the 28 February magnitude 6. Hawaii is another state that few Americans associate with seismic activity, but in fact it has experienced extraordinarily severe earthquakes.

Near Kau on the southern part of the island of Hawaii, on 2 April an earthquake with magnitude of about 8 occurred that may have produced the highest Mercalli intensities of any event in U. Near the epicenter the shaking destroyed stone buildings and threw wood-frame houses off their foundations Wyss Straw houses with posts in the ground were torn to shreds. First, it seems likely that they may be caused at least indirectly by volcanic activity. After the earthquake a tsunami occurred along the Kau-Puna southern coast of the island of Hawaii.

Survivors reported that the wave swept in over the tops of the coconut trees at a height of at least 20 meters and drowned forty-six people. After the earthquake a tsunami that reached a maximum height of In western states other than California, Nevada, Montana, Washington, and Hawaii, both the maximum size of historical earthquakes and the potential hazard are comparatively low. The only earthquake with magnitude of 7 or greater occurred on 28 October at Borah Peak, Idaho, with a magnitude Mw of 7.

Although it has not experienced a severe earthquake since the Mormons arrived more than a century ago, it is situated near the potentially dangerous Wasatch Fault. Earthquakes with magnitudes in the 6. In the Yellowstone Park region of Wyoming, one magnitude 6 aftershock followed the Hebgen Lake earthquake.

If you travel abroad, you discover that in most of the world a Yankee is anyone from the United States. In the Southern states, a Yankee is anyone from the Northern states, usually meaning any state north of the one you are in. In any case, the indisputable fact is that only two or possibly three areas east of the Rocky Mountains have experienced earthquakes with magnitudes above 6 in historic times.

As mentioned previously, between December and February this area had three extraordinary earthquakes with magnitudes of about 8. The earthquakes caused inordinate havoc in the epicentral region as riverbanks caved in and islands disappeared or were formed. The area of strong shaking was two to three times larger than that of the Alaska earthquake and ten times larger than that of the San Francisco earthquake.

The quakes were felt in many cities along the Atlantic coast, frightening people in Washington, D. The largest, on 31 October , had a magnitude of about 6. In the twentieth century the three largest occurred in , , and and had magnitudes between 5. Since a network of seismograph stations was established in the New Madrid region in , no earthquake with magnitude of 5 or greater has occurred Johnston and Schweig In the twentieth century the record of seismic activity near New Madrid is similar to that in the Texas Panhandle, which has also experienced three magnitude 5 quakes.

The second place in the eastern United States where a relatively large historical earthquake has occurred is Charleston, South Carolina. This had a magnitude of about 7 and struck on 1 September This quake killed about sixty people and damaged or destroyed many buildings; in Charleston an estimated 14, chimneys were toppled. An unusual feature was the widespread occurrence of sand craters and the ejection of sand in the epicentral area. Much of Charleston had been built on reclaimed land, and this undoubtedly added to the damage see sidebar 4. As in the New Madrid area, Charleston has experienced no serious earthquakes since In the twentieth century, the Charleston area had several quakes with magnitudes between 4.

However, they mostly occurred in colonial times, making their sizes and exact epicenters subject to dispute. For example, on 18 November an earthquake was felt strongly around Boston and Cape Ann, Massachusetts. It shattered or threw down more than 1, chimneys and was felt from Nova Scotia to Maryland. Sailors on ships at sea thought they had run aground, and it generated a tsunami that caused minor damage as far away as the West Indies.

This earthquake is loosely related to a zone of large-earthquake activity that extends eastward from the St. Northern New York state experienced earthquakes with magnitudes between 5 and 6 in and , and earthquakes with magnitudes 7 have occurred in Quebec—most recently in —and off the Grand Banks of Newfoundland in Elsewhere in the east, historic earthquakes are all smaller than 6.

Indeed, in some states, the largest known earthquakes are almost laughably small. States where the largest known earthquakes have magnitudes between 4 and 5 include Georgia, Michigan, Mississippi, Pennsylvania, Vermont, and West Virginia. In Rhode Island the largest historical earthquake occurred on 11 March and had a magnitude of about 3.

In Maryland the largest historical earthquake occurred on 19 January and had a magnitude of only 2. With two quakes in the twentieth century in West Texas with magnitudes between 5. Historically, it clearly does not have very damaging earthquakes with magnitudes of 7 or so as do states like California, Washington, Montana, Missouri, South Carolina, and Massachusetts. However, unlike states such as Maryland, Louisiana, Michigan, or South Dakota, Texas does occasionally have quakes that could be very damaging if they occurred near an urban area.

The remarkable lack of seismicity along most of the Gulf Coast, coupled with a pattern of seismicity in the Panhandle that resembles the pattern in the New Madrid area, gives Texas a split personality with respect to earthquake risk. It is both a state with low earthquake risk and a state with moderate earthquake risk. Reported magnitudes are often highly variable for very large earthquakes and for earthquakes that occurred prior to about Thus there is considerable disparity among lists that rank very large earthquakes. This gives Maryland the distinction of being the state with the smallest largest earthquake.

Strangely enough, Frohlich has never actually experienced an earthquake large enough or close enough to be felt, even though he has been employed as an earthquake seismologist for three decades. Moreover, while it has a land area smaller than California, it has million citizens.

This high population density compounds the risk for example, an earthquake with magnitude MS of 8. On the other hand, the , citizens of tropical Vanuatu, with a land area much smaller than Japan, experience large earthquakes more frequently. However, in Vanuatu earthquake risk is not especially great, as most people live or work in one-story buildings that are not severely damaged when large earthquakes occur. This chapter will not present a comprehensive summary of the seismicity and hazard for the entire earth.

We assume most readers do not need to determine the relative levels of seismic risk for, say, Turkey and Chile. This is partly 52 Sidebar 4. Over the entire earth, the number of earthquakes with magnitudes of 8 and greater is less than 1 each year. Each year approximately 10 earthquakes of magnitude 7 or greater and earthquakes of magnitude 6 or greater occur table 4. Each year there are more than 1, earthquakes of magnitude 5 or greater, 10, of magnitude 4 or greater, and so forth.

However, these smaller earthquakes are only recorded by seismograph stations situated sufficiently near the epicenter; thus many such earthquakes that occur in remote areas on earth are not recorded, located, or catalogued by anyone. The fact that small earthquakes are very frequent but mostly go unrecorded makes global counts of earthquakes in the twentieth century meaningless unless the count is restricted to all earthquakes with magnitude greater than about 7.

Only since about has the global seismograph network been able to record all earthquakes with magnitudes of 6 and greater. In some geographic regions earthquakes have affected and will increasingly affect the economic and political milieu. This is aggravated by the tendency for global population growth and for industrialization to be concentrated near the oceans, often in coastal and island regions such as Japan, Taiwan, the Philippines, and Indonesia, which regularly experience severe earthquakes. Occasionally legitimate scientists debate this.

The problem is that we only have data for the whole earth for about the past one hundred years, since seismographs were invented. And seismograph design changed so much between and that there may be errors in magnitude estimates for some large earthquakes. Considering the uncertainty caused by these problems, no clear evidence indicates that the rate has changed. But it is possible that when much more data are available scientists will find that global rate changes sometimes do occur.

The authors of this book do not like to get involved in religious arguments; but, quite honestly, we see no scientific evidence of an increase. Earthquake rates may not be increasing, but earthquake risk surely is. In these areas, earthquakes that might have hurt nobody one hundred years ago will cause great damage and loss of life when they occur in the twenty-first century.

For example, consider the 20 September earthquake in Taiwan. Very Big Earthquakes What was the biggest earthquake ever? The biggest ever recorded by seismographs occurred on 22 May in Chile. It had a magnitude Mw of 9. In some places this quake caused vertical uplifts as large as 6 meters.

The second biggest earthquake, with a magnitude of 9. Theoretical calculations suggest that the Chile and Alaska earthquakes are just about as large as possible for planet Earth. Areas experiencing subsidence dark shading and uplift light shading associated with the Chile earthquake of top and the Alaskan earthquake of bottom.

For a magnitude 2. If we calculate the scalar moment of this earthquake as described in chapter 1 and convert the moment to magnitude as in table 1. Larger earthquakes would have to rupture even longer faults with an even greater average slip. What about very large earthquakes that occurred prior to the invention of the seismograph? For several reasons, our knowledge of such events is uncertain and very incomplete.

Some very large earthquakes occur in unpopulated areas, do little or no damage, and go unnoticed. We know that the very largest earthquakes occur in areas such as the Aleutians, Chile, and Japan where the rigid plates are moving toward one another. Many of these areas, such as the Aleutians, have only been occupied for a century or less by literate peoples; indeed, comprehensive records document earthquake activity prior to for only a small fraction of the earth. Nevertheless, there is every reason to believe that on the average, earthquakes with magnitude 9 or greater do occur somewhere on the earth once or twice per century.

The quite frequent occurrence of magnitude 8 earthquakes in South America and Alaska suggests that the Chile and Alaska earthquakes are not isolated incidents. However, only rarely can we determine the time and magnitude of pre earthquakes, as this requires a combination of historical records that prove a very large earthquake did occur and geologic proof that it caused uplift or subsidence over a very large geographic area.

An example of this is the recent assertion that the tsunami that struck Japan on 26 January originated from a rare, very large earthquake in what is now Oregon and Washington. But are measures such as magnitude or scalar moment the right ways to determine which earthquake is biggest? Even this is imprecise. To paraphrase a recent U. On Hawaiian coasts, for example, earthquakes in Alaska in , , and produced tsunami waves that inundated some coastal areas to depths of 4 meters or greater Lander and Lockridge In Japan, 16, km distant from Chile and almost halfway around the world, people were killed a full day after the earthquake occurred when the tsunami arrived.

The most common, direct sensations felt at great distances from large earthquakes are slow, swaying motions. These motions can make chandeliers or hanging objects swing, allow people in tall buildings to sense vague, queasy feelings, and cause sloshing in swimming pools or harbors. Sloshing produced by surface waves from the Alaska earthquake sank boats in several bayous in Louisiana, 5, km from the epicenter. This earthquake had a focal depth of km, making it the largest earthquake with such a great depth that has occurred in the twentieth century.

Texas Earthquakes (Peter T. Flawn Series in Natural Resource Management and Conservation)

Very Bad Earthquakes What is bad? When the above-mentioned 9 June Bolivia earthquake occurred, it was the largest that the world had experienced since Yet even though it occurred on land and was felt over the entire continent of South America, it apparently caused remarkably little damage and few or no fatalities,4 other than breaking numerous windows in La Paz. Other recent very large earthquakes caused little or no damage simply because they occurred in very remote areas. For example, both the Balleny Islands earthquake of 25 March Mw 8. The largest very deep earthquake known, with a magnitude MW of 8.

The seismic body waves from this quake were felt by humans at greater distances than any other earthquake known. Filled circles indicate cities in North America where the earthquake was felt. Plus symbols indicate points where strong P waves are expected to arrive at the surface for an earthquake of this type. Apparently the quake was felt in the northern United States and in Canada at distances between 6, km and 9, km dashed lines partly because it was so deep and partly because its type allowed strong P waves to surface there.

Clearly, people are what makes an earthquake bad—when lots of people are killed or injured table 4. Tangshan had a pre-quake population of about a million people; the main industry was mining. Most of the structures in Tangshan were multiple-story, unreinforced brick and concrete buildings that collapsed during the quake.

Very large twentieth-century earthquakes. Labels with dates indicate locations of significant earthquakes mentioned in the text. The map also shows the boundaries of the principal tectonic plates. National Geophysical Data Center A Estimates of loss of life from the worst earthquake disasters are very unreliable; understandably, when tens of thousands of people are dead and most buildings are in ruins, there are more important things to do than to count bodies. Most experts agree that the most deadly earthquake in historical times occurred in Shanxi Province, China, in ; about , lives were lost.

The two principal factors affecting damage are: Thus, often relatively small but deadly earthquakes occur in regions of dense population where buildings are of unreinforced adobe, stone, or concrete; these structures fall easily and crush inhabitants. An example is the Managua, Nicaragua, earthquake of 23 December ; it had a magnitude MS of only 6. We can well imagine what quakes the residents of Tangshan, China, or Managua, Nicaragua, would choose, and most U. However, a better candidate in some ways is probably the Lisbon, Portugal, earthquake that occurred on the morning of 1 November In the twentieth century Candide has been rewritten as an opera, with music by Leonard Bernstein, and as the comically pornographic novel Candy by Terry Southern and Mason Hoffenberg.

On the morning of 19 September an earthquake with magnitude 8. The earthquake and an accompanying 2-meter tsunami caused some damage in the epicentral area at a few tourist resorts and industrial estates. Why was the damage worst so far away from the epicenter? Damage to structures depends both on the type of construction and on the properties of the material that anchors the foundation.

Experience from many earthquakes teaches us that shaking intensity is amplified for structures built on loosely consolidated sediments. Thus the worst damage often occurs when cities are built on dried-up lake beds. When the Aztecs settled in what is now Mexico City in they chose a low-lying island in the western shallows of a lake because it was easy to defend. When the Spanish took the city in they chose to drain the lake, and today about half of Mexico City occupies the area of the drained lake.

In the earthquake caused little damage in buildings situated on hard rock south of Mexico City, even though earthquake waves travel through hard rock with little loss of energy. But within the city the lake bed subsoils had just the right depth and mechanical properties to trap earthquake energy and destroy buildings with six or more floors. Another earthquake-prone city built on a former lakebed is Managua, Nicaragua, where 6, people died in an earthquake in Elsewhere, unusually severe earthquake damage often occurs when humans build structures on reclaimed land.

In many coastal cities when land becomes scarce people manufacture new land by filling in shallow areas near the coast with loose earth and gravel. In the Loma Prieta earthquake, the worst damage took place in the Marina District of San Francisco, which early this century had been built on land reclaimed from the sea. Unlike the earth, the Moon does not have tectonic plates. However, it does have regular, shallow quakes caused by the heating and cooling of its surface. Just as the gravitational pull of the Moon creates terrestrial ocean tides, the much more massive earth creates strong tidal forces on the Moon Nakamura, Latham, and Dorman Elsewhere in our solar system, the situation is not so clear.

The instrument at left is identical to one of the lunar seismographs. But for now we have no seismographs in place to be sure. Incidentally, the edition of the Guinness Book of World Records has only four entries concerning earthquakes. News media reported no fatalities. The area that is now the Marina District was originally a tidal marsh. An enormous amount of brick, rocks, and mortar needed to be disposed of, and this was just a convenient place to put it.

This article does not explicitly state that the Viking seismometer did not record any marsquakes. Nevertheless, our discussions with the knowledgeable members of the seismology community indicate that the surface emplacement of the Viking seismometer made it a very low-gain instrument that measured mostly wind-generated phenomena and that it is unlikely any of the recorded signals were of seismic origin.

In defense of the authors of the published article, they had little control over the design decisions that placed the Viking seismometer on the surface instead of some distance underground, where it might have been able to measure seismic activity. He then turned the bottle on its side, carefully pointing it away from partygoers toward a corner, and methodically slid the backside of the knife up the side of the bottle until it hit the glass lip on the bottle just below the cork.

The clean fracture across the neck of the bottle corresponds to the fracture of rock along a fault surface during an earthquake. For fracture to occur there must be: The suddenness of rock fracture is an important feature of an earthquake. Any solid material—a pencil, an ice cube, or a rock—will break or deform if you squeeze it or stretch it enough. But if it breaks in an instant, the sudden motion and the elastic wave that travels away from the breaking point are what we know as an earthquake.

As with the champagne trick, this can hurt people if they are in the wrong place. The party trick of opening a bottle of sparkling wine with a heavy kitchen knife shares many features in common with an earthquake. For either to occur, there must be a source of stress, a geometry that concentrates the stress, and a trigger. Natural Earthquakes and Plate Tectonics What natural processes cause earthquakes? Some of the motion occurs as gentle creeping or sliding, without any earthquakes. At other times the plate edges stick to one another and the plates store elastic energy as they continue moving.

When the stuck part suddenly comes unstuck, you have an earthquake. If the stuck region is large and has been stuck for decades or centuries, you have a large earthquake. If people are hurt or property is damaged, you read about it in the papers. Of course, attributing earthquakes to plate motion avoids the real question— what causes these plates to move? When a material is heated from beneath, this heating causes the warmer bottom material to rise while the cooler material at the top sinks.

Convection is just the technical name that describes this whole process of heating, rising, and sinking. Heated, solid rock expands, becomes less dense, and moves upward. And just as in a pot of soup or a thunderstorm, the whole motion gets organized into big rolls of up-, down-, and sideways-moving material. In the earth this sideways moving material is the plates, and it is the convective rolls beneath which move them.

If the rock that forms Enchanted Rock, Texas see Figure 5. For example, the deepest parts of the ocean and the deepest earthquakes occur where the cold material is sinking. These so-called deep ocean trenches usually have chains of volcanic islands nearby—the Philippines, Japan, and the Aleutians in Alaska are familiar examples. One such region extends along the middle of the Atlantic Ocean, passing through Iceland and the Azores Islands. Convection is the scientific name used when heating from below causes a liquid, gas, or solid to expand, become less dense, and rise vertically.

Subsequently, it cools and sinks, so the whole process forms a continuous pattern of up- and down-going motion. Thunderstorms and boiling soup are familiar examples of con- vection in liquids and gases. Convection of solid material within the earth is what drives plate tectonics. Mid-ocean ridges mark the location of hot rising material; at the surface it cools into plates and moves away; where it is cool and dense enough to sink, a deep-ocean trench forms.

At these shallow depths the rocks are cold and brittle, allowing them to fracture suddenly when they are under sufficient stress. At greater depths the temperature is higher and stress causes the rocks to deform slowly by creep or flow, so no earthquakes occur. Generally, earthquakes do not occur if the temperature is above about C. Thus in Japan, the Philippines, South America, and several other places, some earthquakes occur down to depths as great as km. Other Natural Earthquakes Texas is in the middle of a tectonic plate, so how can there be earthquakes in Texas?

These include a few very large and damaging earthquakes such as the — New Madrid, Missouri, sequence, the earthquake in Charleston, South Carolina, and the Hebgen Lake, Montana, earthquake. Of course, the convection that drives tectonic plates can cause stress in the middle of plates—not just at their edges. So plate tectonics could be at least partly responsible for mid-plate earthquakes in Texas and elsewhere. However, several other natural processes can stress rock enough to cause earthquakes.

While it is free to contract vertically, in order to contract horizontally it has to break, usually along a pre-existing weakness such as a fault. Erosion does the same thing in reverse. Enchanted Rock is a meter-high granite batholith in central Texas that is a favorite spot for hikers, campers, and rock climbers.

Some solid materials—like silly putty, pitch, or ice in glaciers— can flow even though they are not liquid. The lava that erupts from volcanoes is created by thermal and chemical processes in the earth and does not originate from any vast reservoir in the interior. Thus magma is formed in regions where there is convective sinking or elsewhere when near-surface rocks are heated. It is free to expand vertically but is constrained horizontally by neighboring rock; the differential expansion produces stress and, sometimes, earthquakes.

For all kinds of reasons, rock everywhere is under stress. Even if some of the details are wrong, that does not mean the theory is wrong. Gulf of Mexico earthquakes.

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In and in , earthquakes with magnitude of about 5. These earthquakes may have occurred because, over time, sediments deposited by the Mississippi River became so thick and heavy that they produced enough stress to break the underlying bedrock see Frohlich The circles show the locations of the earthquakes, and the contour lines indicate the thickness in meters of Mississippi Fan sediments as reported by Weimer Army Corps of Engineers drilled a well to a depth of 3, m to dispose of chemical wastes generated at the Rocky Mountain Arsenal, a military installation situated a few kilometers northwest of Denver, Colorado.

Injection began in April and continued for four years, during which million liters of waste were injected into the well. And less of the material reaches the environment than with other disposal methods in which further human handling inevitably results in some environmental contamination. The Army discontinued the injections in February This incident would probably be of interest only to scientists Healy et al.

These were large enough to pose a genuine hazard and produced legitimate public concern among the citizens of Denver. How does injection cause earthquakes? Because the stresses that cause the earthquake are of tectonic origin and not caused by the injection itself, the earthquake can be large—with a greater magnitude and more energy than any process attributable solely to the injection. Earthquakes caused by humans.

Comparison of volume of fluid injected and the number of earthquakes observed at the Rocky Mountain Arsenal near Denver, Colorado. Note that earthquakes were most frequent in , , and , when fluid injection rates were highest; however, they continued even after injection stopped in Fluid injection has actually been suggested as a means of controlling earthquake hazard. Imagine the legal and political furor that would ensue if the government began such a program and then a magnitude 8 quake occurred.

Our records indicate that altogether about earthquakes with epicenters in Texas were felt by Texas residents table 9. Of these, 19 had epicenters within producing oil or gas fields, and 17 more had epicenters within 3 km of a field. We have evaluated these and have concluded that 22 probably were induced by human activity.

About 5 percent of Texas land area lies within a major oil or gas field. One should not conclude that seismic activity is induced unless earthquakes begin only after a field starts producing and unless the pattern of felt reports suggests that the quakes occurred at relatively shallow depths within the field. Davis and Frohlich Earthquakes Induced by Fluid Withdrawal In a few cases the removal of natural gas, oil, or water from underground strata appears to cause earthquakes.

The largest such quakes known are a remarkable series of three MS 7. By gas production had reached 20 billion cubic feet per year Simpson and Lieth How could something as innocuous as removing a gas cause an earthquake? In the Gazli case, a total of more than billion cubic feet of gas was removed; at atmospheric pressure this corresponds to a cube more than 2. If compressed and stored as a liquid, this would occupy a cubic tank with dimensions of about meters on each side.

Removing this much material is bound to affect the stress along underground faults in the region, which ultimately may slip to readjust the stress. To obtain magnitude 7 earthquakes as in Gazli, however, the region must experience a considerable amount of regional tectonic stress as well Plotnikova et al. Removing gas, oil, or water for irrigation or human consumption normally causes no earthquakes whatsoever. During local residents felt about tremors, and in a magnitude 5 earthquake occurred. Seismographs installed to monitor the activity indicated that most of the earthquakes had focal depths of 6 km or less and were concentrated along existing faults within 25 km of the lake.

The earthquakes continue up to the present day; by the s more than 10, earthquakes had been recorded, including several with magnitude of about 5. Subsequently, as more large and deep reservoirs have been constructed around the world, reservoir-induced earthquakes have become a relatively common phenomenon. Indeed, induced earthquakes with magnitude exceeding 6 have occurred near reservoirs in China, India, Greece, and along the ZambiaZimbabwe border in Africa. The largest of these, a magnitude 6. Earthquakes with magnitudes of 3 or greater are associated with about a quarter of all reservoirs with depths exceeding meters, and some reservoirs with depths of 50 meters or less report induced seismic activity Gupta Reservoirs can induce earthquakes by two mechanisms.

First, the weight of the water alone produces stress in the rock strata beneath and adjacent to the reservoir. If faults in these strata are almost ready to fail, the additional stress may trigger an earthquake. For both mechanisms the earthquake is most likely to occur while or within a few years after water depth changes substantially. Note that of the listed earthquakes, only the Borger and Fashing events occurred after deliberate impoundment commenced.

However, of these, only the Borger earthquake and the Fashing earthquake actually occurred after deliberate impoundment of water began. In both cases these events occurred in the same locations as several earthquakes did before the dams were constructed. Thus, it is unlikely that either of these earthquakes was reservoir-induced. In Texas a more likely candidate for a reservoir-induced earthquake is the magnitude mbLg3. Spence Reservoir, which was created by a meter-high dam completed in We are unaware of any previous seismic activity in this area.

Are faults more likely to slip when gravitational forces from several astronomical bodies all pull in the same direction? Thus the sun and the moon are much better candidates for triggering earthquakes than any combination of planets. This is why the height of the ocean tides depends so strongly on the positions of the sun and moon but not the positions of the planets. When severe earthquakes do occur near the full moon or new moon, it is just a coincidence Heaton ; Rydelek, Sacks, and Scarpa ; Vidale et al.

Some investigations of earthquake catalogs have found weak seasonal, weekly, or daily variations in the frequency of earthquakes reported, but this almost cer- 78 T E X A S E A RT H Q UA K E S tainly occurs because seismograph stations are more sensitive and can detect smaller quakes during quieter periods. In many parts of the United States, the most common local events recorded by seismographs are quarry blasts.

For safety reasons, these are typically set off in the late afternoon, just before quarry workers leave work for the day. For obvious reasons, almost all of these have been clustered in a few remote geographic locations, including Nevada, Novaya Zemlya, and Tahiti. Finally, sometimes sonic booms produced by supersonic aircraft are mistakenly reported as earthquakes.

Other parts of the United States experienced similar blasts over the next few days that newspapers speculated might be caused by earthquakes, exploding meteors, or sonic booms. Although several Air Force bases denied that any of their jets were responsible, Convair at Fort Worth, Texas, later admitted to testing a B supersonic bomber in the Panhandle at the time of the tremors. In our experience, people who see the champagne trick performed fall into two categories: If you are in the second category, please read the following four suggestions carefully.

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So always be sure to do this outdoors and be sure that the bottle is not pointed in a direction where there are people. Cities where people reported feeling or hearing the 10 February Panhandle event. Although this was listed in several catalogs as an earthquake, the linear pattern suggests that this event was probably a series of sonic booms occurring along the flight path of a supersonic aircraft.

The fracture is triggered by the momentum in the knife motion and not by any kind of cutting action. See Zoback and Zoback for a summary of stress in the continental United States. Do you want to sue somebody when an earthquake occurs? For a discussion of the legal aspects of liability for induced earthquakes see Cypser and Davis and The referenced article also lists criteria for deciding whether an earthquake is injectioninduced. Over the past century California has experienced approximately nine earthquakes with magnitude of 7 or greater; we presume there will be similar activity in the century to come.

At the rate of nine quakes per century, the chances are better than even that at least one will occur on any particular day of the week, such as a Saturday. But do these qualify as earthquake predictions? Not really, since they are just restatements of facts about earthquake activity in California, phrased so that they sound like predictions.

So how about this assertion? An earthquake with magnitude of 7. And of course, people only remember their predictions if they come true. There have been extraordinarily few successful predictions of the time, location, and size of future earthquakes. The day before a magnitude 7. Nobody knows the day, year, or even the decade when the next earthquake with magnitude of about 8. However, the available scientific evidence indicates that, on the average, such earthquakes strike California about every 50 — years.

Why do scientists believe that great earthquakes occur in California every 50 — years? Prior to the quake, a great earthquake occurred in near what is now Los Angeles in southern California. Before that, there are no historical records of earthquakes; however, near the epicenter geologists have carefully excavated streams along the fault that were offset by previous large earthquakes Sieh By using radioactive dating methods on bits of wood deposited by the streams before and after the offsets, they determined that at least eight large earthquakes occurred, at approximately a.

Although each individual date had an uncertainty of about 50 years, these data indicate an average interval of years between quakes, with a range from 55 to years. Since these data apply only to southern California, it is plausible that for the entire state the average repeat time is somewhat less about 50 — years. Because of these efforts the city suffered little loss of life.

How were Chinese seismologists able to make this prediction? Part of the answer is that China has the most extensive earthquake prediction program anywhere in the world, involving about 10, full-time workers and several tens of thousands of part-time volunteers. By mid seismologists had concluded that an earthquake with magnitude of 6 or greater would occur in the province between and At a State Seismological Bureau conference in January seismologists announced that an earthquake of magnitude 5.

On 1 February a small earthquake M 0. On the morning of 4 February the Provincial Revolutionary Committee began disaster prevention measures in Haicheng. On the afternoon of 4 February the foreshock activity subsided. When the earthquake did occur at 7: Estimates indicate that there would have been , casualties without the correct prediction Raleigh and others In a twist of cruel irony, though, only a year later Chinese scientists failed to predict a magnitude 7.

Tangshan is an industrial city of about one million inhabitants in eastern China, about km from Beijing. When the earthquake occurred at 3: Magnitude and time of occurrence for foreshocks recorded prior to the Haicheng, China, earthquake of 4 February In Haicheng anomalies had been detected several months in advance and had increased in intensity several days before the earthquake.