Earthquake History of Nevada

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Earthquake History of Nevada

Nevada ranks among the most seismically active States. A number of the larger shocks have produced some spectacular examples of surface faulting; these include shocks at Pleasant Valley (1915), Cedar Mountain (1932), Excelsior Mountain (1934), Rainbow Mountain (1954), and Fairview Peak - Dixie Valley (1954). Although these events are classied as major earthquakes in terms of magnitude, no fatalities were reported and building damage was minimal because of the sparse population of the epicentral areas.

The earliest reported earthquake in Nevada occurred in 1851. A newspaper article in 1865 cited reports of an earthquake 13 years earlier near Pyramid Lake. The account stated that great cracks opened from which water spouted 100 feet high. Large landslides were also reported.

On October 2, 1915, three strong earthquakes within about 7 hours disturbed a large part of northern Nevada. The third tremor had an estimated magnitude of 7.75. It destroyed or seriously damaged many adobe houses in Pleasant Valley. Most of the damage was confined to the towns of Kennedy, Lovelock, and Winnumucca. The earthquake was felt over a very wide area - from Baker, Oregon, to San Diego, California, and from the Pacific coast to beyond Salt Lake City, Utah, an area of about 1,295,000 square kilometers. A scarp 1.5 to 4.5 meters high and 35 kilometers long, was formed parallel to the base of the Sonoma Mountains. About 100 aftershocks followed the main earthquake.

An earthquake of magnitude 7.3 originated in west-central Nevada on December 20, 1932. The epicentral area, near Cedar Mountain, was almost uninhabited. Two cabins, one of stone, and the other of adobe, were destroyed, and mining property was damaged. Many chimneys were thrown down at Mina and Luning. At Hawthorne, the shock cracked and threw down chimneys. Extensive and complicated faulting occurred northeast of Mina, over an area of about 60 kilometers long and 6 to 14 kilometers wide in the valley between the Cedar and Pilot Mountains. The total felt area was approximately the same as that of the 1915 shock.

About a year later, on January 30, 1934, a magnitude 6.5 earthquake which centered in the Excelsior Mountains area about 80 kilometers west of the 1932 zone, again caused some damage at Mina. The collapse of some adobe buildings at Marietta was also reported. Several foreshocks were noted; the strongest had a magnitude of 5.5 and occurred about an hour before the main earthquake. Slight damage at Mina resulted from this foreshock. A small fault scarp 12.5 centimeters high and about 1,500 meters long was formed on the south slope of the Excelsior Mountains. The earthquake was felt widely over Nevada and in parts of California and Utah, an area of about 285,000 square kilometers.

The Rainbow Mountain area in the Stillwater Range, about 25 kilometers east of Fallon, was the origin of a series of earthquakes in July and August 1954. The first strong earthquake on July 6, magnitude 6.6, was damaging at Fallon; it was followed by a magnitude 6.4 shock about 11 hours later and by a series of smaller aftershocks. Another large earthquake, magnitude 6.8, on August 23 caused additional damaged at Fallon. It too was followed by many aftershocks. Ground breakage was traced for about 40 kilometers.

On December 16, 1954, a major earthquake of magnitude 7.1 occurred about 50 kilometers east of the epicentral region of the July - August shocks, near Frenchman's Station. A magnitude 6.8 aftershock followed 4 minutes later. Intensity X was assigned to the spectacular surface ruptures which occurred in two major fault zones; one on the west side of Dixie Valley along the east base of the Stillwater Range and the other on the east side of Fairview Valley in the Clan Alpine Range. Faulting extended north and south for a linear distance of approximately 90 kilometers. Vertical movement of 1.5 to 4.5 meters was measured in Dixie Valley. About 2 to 6 meters of vertical movement and about 1 to 4 meters of horizontal movement were measured near Fairview Peak. Because the epicentral region was sparsely populated, this potentially destructive earthquake caused relatively little property damage. At Fallon, a few toppled chimneys were noted. Chimneys twisted and fell at Austin. At Sacramento, California, located about 265 kilometers distant, the shock caused an estimated $20,000 damage to a large underground water tank at the city's filtration plant. Some damage was also reported at the city's sewage disposal plant. The shock was felt throughout Nevada and in parts of Arizona, California, Idaho, and Oregon, an area of about 520,000 square kilometers. Again, a long series of aftershocks followed.

Only Nevada's major shocks have been listed here. A study by the University of Nevada in 1965 tabulated 1,173 "felt" events with epicenters within the State during the 1852 - 1961 period. Another 586 having magnitudes greater than 4.0 were recorded and probably were felt by some residents. Approximately 220 were reported in nonspecific terms (for example, "several aftershocks were felt"). A general increase in the number of events reported each year has been correlated with the upward trend in population.

Abridged from Earthquake Information Bulletin, November - December, 1974, by Carl A. von Hake.

Questions and Answers on Earthquakes in Nevada

Q: Why does Nevada have earthquakes?
A: Nevada has both small and large earthquakes. Nearly all the mountain ranges in the state are growing, one earthquake at a time. (topographic map)

Q: Could a big earthquake like they have in California happen in Reno?
A: Yes, but not as often. Reno had a nearby magnitude 6.4 earthquake in 1914, and we believe we had a magnitude 6.7 earthquake very nearby in 1869. The potential exists for earthquakes of magnitude 7.0 or a little larger in the Reno area. (Earthquakes in Reno-Carson City map)

Q: How many earthquakes are there in Nevada?
A: There are thousands each year that are too small for anyone to feel. There might be tens to over one hundred earthquakes over a year in Nevada and eastern California that are large enough to be felt. On average an earthquake that is strong enough to be damaging, if it strikes a populated area, occurs about every three years in this region. (seismicity map; earthquake search)

Q: Where are the faults in Nevada?
A: We have found active earthquake faults in every part of Nevada. The area just east of the Sierras might have the most activity. There is an active fault at the base of nearly every mountain range in the state. So everyone in Nevada lives no more than several miles from an earthquake fault. (fault map of Nevada)

Q: Are there faults near Reno?
A: There are at least two faults running into the city limits that may be capable of a large, damaging earthquake of magnitude 7 or more, larger than the Northridge earthquake in January 1994. There are many more apparently smaller faults. (fault map of Reno-Carson)

Q: Are there active faults near Las Vegas?
A: Yes. Just as many as in any other part of Nevada. But they may not have earthquakes as often as in the other areas. (fault map of Las Vegas)

/a>Q: Are there faults near Las Vegas that could produce a magnitude 7 earthquake? Are there more earthquakes in Nevada than in Arizona or New Mexico?
A: There are faults in the region around Las Vegas that have the potential to produce strong earthquakes on rare occasions. Rare means that the average time between the large earthquakes on any one of the faults is at least 1000-10,000 years. We do not know when the next one will happen, of course.

There are also active faults with long average times between earthquakes in some parts of Arizona, and some parts of New Mexico. On average, Arizona and New Mexico both have fewer earthquakes than Nevada, but a strong Nevada earthquake is more likely to be close to Reno than to Las Vegas, so a state-wide average doesn't tell you anything about the hazard faced by Las Vegas.

Q: Do all earthquakes occur on faults?
A: Yes, but it is very common for earthquakes in Nevada to occur on faults that deeply buried, and thus not visible on the ground surface.

Q: What should a small earthquake mean to us?
A: It's good to remind Nevadans that we have earthquake hazards, and of the simple things we can do to be prepared.

Q: Does a local earthquake make another or a larger earthquake more likely?
A: Yes, for the next five days. But the chance is not high. Right after the earthquake, there is only about 6% chance of another earthquake that size or larger, and about 3% for an earthquake that is noticeably larger. The chance is decreasing all the time, and five days after the earthquake, it will be back essentially to normal.

Q: What does an earthquake somewhere else in the world mean for northern and western Nevada?
A: It will not have any direct effects. Events that far away are not capable of affecting earthquakes in Nevada.

Q: Could a big earthquake in California cause earthquakes in Nevada?
A: In the past we didn't think so, but now we know that the 1992 Landers earthquake caused minor events all the way up into southern and western Nevada. Any other magnitude 7 earthquake might be big enough to repeat that. We do not expect any earthquake smaller than magnitude 7 to trigger tiny events in Nevada.

Q: Do we have as much earthquake risk here in Nevada as they do in California?
A: We could have earthquakes just as large or larger than the Northridge or Loma Prieta earthquakes, but less than half as often. We do not expect magnitude 8 earthquakes here (like the 1906 San Francisco quake).

Q: How many and what size of earthquakes do we have near Reno?
A: Just within 25 miles of Reno, history records 16 serious (M>=5.5), potentially-damaging earthquakes since 1869, or more than one every ten years. Sometimes there are quieter periods; but there was no predictive significance to the fact that the last one before the September 1994 earthquake south of Gardnerville, was over 28 years before, in 1966 near Truckee. (paper on Reno earthquake occurrence)

Q: What would happen during an earthquake in Reno/Carson?
A: The Nevada Earthquake Safety Council has developed a scenario, or a description of what could happen, if the nearby Genoa fault were to rupture