An Introduction to Nevada's Earthquake Hazards

Spring 1989

The state of Nevada is located in "earthquake country." It lies within the Basin and Range structural and geomorphic province, a region that is actively extending, or being pulled apart in roughly a northwest-southeast direction. The Basin and Range province is riddled with active faults and is one of the most seismically active regions in the United States.

Nevada, along with California, has been subject to many large earthquakes in the last 150 years. The average occurrence of earthquakes of magnitude 6 and greater in Nevada is about 10 years. The average occurrence of earthquakes of magnitude 7 and greater that have strongly shaken the state is about 27 years. The range in time between earthquakes of magnitude 7 or greater is 17 to 44 years, and the last one occurred 35 years ago.

Based on newspaper reports, the earliest reported large earthquake in Nevada's history is one which the Piute Indians believe occurred in the 1840's or early 1850's and which was widely felt in western Nevada. On December 27, 1869, an earthquake of magnitude 6.7 shook down walls in Virginia City and Gold Hill, and is referred to as the Olinghouse earthquake, after the mining district northwest of Wadsworth, where the earthquake is thought to have originated.

The largest earthquake in Nevada's history (magnitude 7.6) occurred on October 3, 1915, and was centered in Pleasant Valley, south of Winnemucca. This earthquake broke the surface in four different places over a distance of 37 miles (60 km). The largest offset of the ground was 19 feet (5.8 m) of vertical movement.

In 1932 a magnitude 7.2 earthquake originated in the Gabbs area and was felt throughout Nevada and beyond, over an area of 500,000 square miles (1,295,000 square km) . This earthquake involved several faults failing in sequence.

Four earthquakes occurred in 1954 that caused damage to buildings in Fallon and ruptured the ground in a spectacular fashion in Dixie Valley and near Fairview Peak, 30 to 35 miles (48 to 56 km) east of Fallon. The July and August 1954 earthquakes occurred along the same fault at Rainbow Mountain, east of Fallon, and had magnitudes of 6.6 and 7.0. On December 16, 1954, two large earthquakes of magnitude 7.2 and 6.8 occurred only four minutes apart at Fairview Peak and Dixie Valley. Faulting of the surface occurred discontinuously from northern Gabbs Valley to Dixie Valley, a distance of 63 miles (102 km). The largest fault scarp was about 23 feet (7 m) high, near Fairview Peak.

Faulting of the ground surface is commonly associated with large earthquakes of magnitude 5.5 or greater. The figure shows earthquakes in and near Nevada which have ruptured the ground surface during the historical earthquake period. One major goal of earthquake hazard mitigation is to avoid locating buildings or other important structures across such faults which might rupture the surface during future earthquakes.

It has been years since the last large earthquake in Nevada (1954), and many Nevadans don't appreciate how high the earthquake potential is. We cannot prevent earthquakes but many steps can be taken to minimize or eliminate the potential hazards of earthquakes. Mitigation measures include building with sound lateral or shear support, anchoring objects inside a home that might topple or fall and injure someone, and being prepared to respond to an earthquake, no matter where you are.

For the past 15 years,the Nevada Bureau of Mines and Geology (NBMG) has had an earthquake hazard program designed to provide the public with information to understand, evaluate, and mitigate earthquake hazards. The University of Nevada Seismological Laboratory maintains a seismographic network in western Nevada and records, analyzes, and catalogs earthquakes in Nevada and eastern California.

NBMG has published an earthquake epicenter map of Nevada, and a number of fault and related hazard maps which are available for urban areas in Nevada including the Carson City, Las Vegas, and Reno areas at scales of 1:24,000. Regional maps are available at a scale of 1:250,000. Other specific seismic hazard investigations conducted at NBMG include studies of the Dixie Valley fault in the IXL Quadrangle (NBMG Bulletin 102), studies of the Quaternary tectonics and faulting at the potential site for high-level nuclear waste storage at Yucca Mountain, and research on the large Basin and Range earthquakes.

NBMG also houses a wide variety of aerial photographs covering the state of Nevada. These may be examined at NBMG by consultants, planners, students, and the general public. Maps and reports from other agencies, such as the U.S. Geological Survey, on Nevada earthquake hazards are also available for inspection.

This spring, a pamphlet titled "Earthquakes in Nevada and how to survive them" will be distributed throughout the state. We encourage you to take a few moments to read this pamphlet, and to take a few of the simple, inexpensive steps to help minimize the possibility of personal injury and property damage from earthquakes.

If we are aware of the tectonic forces responsible for the spectacular landscape of Nevada, and spend a little time preparing for the earthquakes these forces can produce, we can live safely with the earthquakes that will eventually occur.

---Craig dePolo, Research Geologist