Top Ten Important Lessons from Nevada’s Largest Historical Earthquake
On the centennial of the October 2, 1915 Pleasant Valley, Nevada earthquake, it is wise to reflect on this event so we can be better prepared for future earthquakes. It was a powerful magnitude 7.3 earthquake with a remarkable foreshock sequence, dramatic surface rupture, and widespread effects.
We learned these important lessons from this large earthquake:
1) Earthquake Country: The 1915 earthquake underscores beyond a doubt that Nevada is earthquake country and that Nevadans should be earthquake ready. Drop, Cover, and Hold On. Twenty-three earthquakes of magnitude 6 or greater have occurred in Nevada since 1857.
2) Widespread Damage: The Pleasant Valley earthquake caused damage to multiple communities that were as much as 50 miles away. This illustrates that large earthquakes cause widespread damage and can affect many communities at the same time. It is important for emergency managers to be mindful of these possible effects when planning for earthquakes and considering potential available resources.
3) Surface Ruptures: The 1915 earthquake ruptured the ground for over 35 miles and vertically offset the surface by as much as 19 feet. Surface rupture commonly occurs with earthquakes of magnitude 6.5 or larger. When possible, new construction should avoid building across earthquake faults.
4) Foreshock Activity: The 1915 earthquake had an extraordinary foreshock sequence, including earthquakes of magnitude 5.0 and 6.1. Foreshocks are earthquakes that precede a mainshock. Although usually less energetic, foreshock activity has preceded most magnitude 6 and greater historical earthquakes in the state, making Nevada an excellent area to conduct foreshock studies and experimental earthquake forecasts.
5) Foreshocks as Early Warnings: Foreshocks associated with the 1915 earthquake could have triggered a useful earthquake warning. Post-earthquake warnings, such as a statement that over the next 72 hours there is an elevated chance of having an earthquake of equivalent magnitude or larger, can be used to initiate temporary mitigation measures and alert emergency responders. As a natural reaction to the 1915 foreshocks, the Pearce family in Pleasant Valley removed the horses from a barn that collapsed during the mainshock.
6) Liquefaction: During the 1915 earthquake, liquefaction occurred in multiple valleys, damaging roadways. Liquefaction occurs when strong shaking causes water-saturated soils to liquefy, flow, or break up. It is more common in semi-arid Nevada than most people think. Liquefaction can have the largest impacts on buried infrastructure, such as water, gas, and sewer lines, but areas of potential liquefaction can be identified and mitigation techniques are available to eliminate or minimize damage.
7) Active Mountain Building: The 1915 earthquake was a scientific milestone, demonstrating that earthquake movement along faults created the mountains in the Basin and Range Province and that this process is active. Professors from the University of Nevada and Stanford studied and published information on the 1915 earthquake and surface rupture. They also found evidence for paleo-earthquakes of similar size in older fault scarps along the rupture. Dr. J. Claude Jones of the University of Nevada was a great scientist and early seismologist who began the tradition of earthquake research at Nevada universities.
8) Changes in Springs and Groundwater: The 1915 earthquake caused increased flow of springs and new springs within 50 miles of the earthquake according to Dr. Jones. Hot springs were also affected: some hot springs went dry and some increased flow near Golconda; hot spring flow increased near Elko and south of Battle Mountain; and a hot spring went dry and required re-drilling near Carson City. It is hard to predict the effects earthquakes can have on groundwater, but changes commonly occur.
9) Building Damage: Building damage from the 1915 earthquake is similar to what might be expected from strong earthquakes occurring today in Nevada. Seismically vulnerable buildings, like unreinforced masonry buildings, commonly have the most damage and have high earthquake risk.
10) Emergency Response: Nevadans have a tradition of conducting admirable emergency responses to earthquakes. Following the 1915 earthquake, neighbors helped neighbors in Pleasant Valley and local professionals responded effectively. The Winnemucca fire warden checked all the chimneys in town for fire hazard and posted a warning in the local newspaper.