Guest Post: Nevada Bureau of Mines and Geology; Nevada's Great 1915 Earthquake
Enjoy this post put together with information from Nevada Bureau of Mines and Geology about the 1915 Pleasant Valley, Nevada Earthquake on its 100th anniversary. All information was taken from The 1915 Pleasant Valley, Nevada Earthquake website.
Winnemucca was the Nevada community with the most earthquake damage. Several brick and adobe buildings in this area had portions of walls thrown down and some plate-glass windows were broken. Damaged chimneys and building contents occurred throughout Winnemucca. For more detailed information check out The 1915 Pleasant Valley, Nevada Earthquake Centennial website.
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.
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.
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.
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.
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.
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When folks talk about earthquakes most people consider California to be earthquake country, but Nevada gets its fair share of seismic activity too! Northern Nevada was very active geologically during 1914 and 1915, as you can see on this short video which shows activity from 1850-2012. Magnitude 6 and 6.4 earthquakes occurred in Reno during February and April of 1914 and Mt. Lassen had several eruptions between May 1914 and October 1915, occasionally dusting Winnemucca with fine ash.
The Pleasant Valley earthquake of October 2, 1915 was the largest earthquake in Nevada's recorded history. The 1915 Pleasant Valley earthquake was preceded by a rare, highly energetic foreshock sequence that forecasted the ensuing large earthquake. For a detailed description of the sequence check out the October 5, 1915 Silver State Newspaper to read L. Roylance's account of the seismic activity. The mainshock occurred at 10:54pm. Shaking lasted for 40 to 55 seconds over a large area of northern Nevada. Nearly continuous aftershocks created continuous ground motion in Kennedy for at least 15 minutes after the mainshock! It ruptured the ground about 50 miles south of Winnemucca, and left a scar along the range front that was more than 35 miles long. In places, the ground surface was offset vertically by as much as 19 feet.
The earthquake had a magnitude of 7.3 and was felt throughout Nevada as shown on the Modified Mercalli Intensity Map. The most devastating effects of the earthquake were to buildings on ranches in Pleasant Valley where total and partial collapses devastated some homes and barns. Although the 1915 earthquake took place in a rural setting with only a half a dozen ranches in Pleasant Valley, 100% of the people in the Valley were severely impacted by the earthquake.
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| Modified Mercalli Intensity Map of 1915 earthquake. Areas with Intensity VIII to X had partially and totally collapsed buildings, surface rupture from fault movement, and ground cracking. Areas with Intensity VII had shaking strong enough to damage chimneys, within Intensity VI areas walls were cracked, and shaking in Intensity V areas was strong enough to awaken people. |
On the centennial of the October 2, 1915 Pleasant Valley, Nevada earthquake, it is wise to reflect back on this event so that we can be prepared for future earthquakes. Here are some of the important lessons from this large earthquake:
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.
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.
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.
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.
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.
