An ongoing sequence of more than 60 small earthquakes that began in the early morning hours today is centered in the Sun Valley area – they are too small to be felt. But, more than 1,200 people filed "felt reports" following the magnitude 3.7 earthquake in Washoe Valley the night of June 6. The shaking is a gentle reminder that Nevadans live in the third most seismically active state in the nation, behind Alaska and California.
The Nevada Seismological Lab at the University of Nevada, Reno leads the initiative of monitoring, researching and assessing earthquake hazards throughout the state. They also lead the charge about earthquake preparedness.
"These sequences like we are seeing in Sun Valley can either subside or escalate; we've seen it happen both ways in Nevada," Graham Kent, geophysicist and director of the Nevada Seismological Lab, said. "These are common in Nevada, once in a while we've seen them culminate in magnitude 4 and higher earthquakes. It pays to be prepared."
There has been this type of activity in the Sun Valley area before, and while it's likely to not result in a large earthquake, sometimes they do, he said. The Washoe Valley sequence June 6 was short and abrupt, ending in the 3.7 earthquake.
Nevada has dozens of identified earthquake fault systems. The state even shares some faults, and is interconnected, with some California fault systems. And the fault systems haven't been moving as much as expected when looking back at the history of earthquakes in the last 100 years.
Nevada earthquake hazard similar to California
"Our urban area in western Nevada has a hazard approaching the level that is seen near the most active faults in California," said John Anderson, a University of Nevada, Reno professor and lead author of a new paper, which is an outcome of the two-day workshop describing earthquake hazard in Nevada. "We hope that this perspective will encourage residents of our area to undertake sensible actions to be prepared for earthquakes."
In their work to help keep people prepared, and to better understand seismic hazards in Nevada, the Seismo Lab brought together 40 geophysicists, geologists, and engineers - earthquake and ground motion experts - in a two-day workshop to assess the earthquake hazards in the two largest urban areas of Nevada. The workshop was to review ongoing earthquake hazard research in Nevada, discuss technical issues related to Nevada earthquake hazards and identify priorities for future research that will reduce uncertainties and improve the USGS National Seismic Hazard Model. The workshop included contributions from a wide range of earthquake professionals from government, academia and industry.
"The reality is that we hold these workshops to better understand sequences like this, to find a path of understanding of the likelihood of whether they go larger or not," Kent said.
The urban areas of western Nevada have the highest seismic hazard in the state. The Las Vegas Valley has a lower seismic hazard than northern Nevada, but there are higher uncertainties as to hazard level. An expanded geodetic network and continued geological studies of the active faults are needed.
The more distant Garlock and Death Valley and even the San Andreas faults in eastern California impact the hazard in Las Vegas, because the Las Vegas basin amplifies long-period ground motion and prolongs its duration. The report emphasizes that it is very important to better understand the important faults in southern Nevada, including hard to interpret faults that run through the heart of the city.
A quiet 60 years of seismic activity
The most recent 60 years have been quieter than earlier times. All 13 of Nevada's historical earthquakes with magnitude 6.5 or greater occurred in the 102-year period ending in 1954. Of the 44 known earthquakes with magnitude 6.0 or greater, only five have occurred since 1960, while 15 would be more consistent with the prior historical rate.
The summary of the workshop comments that there is some reason to believe that the pre-1960 earthquake rates are more typical of what we should expect in the future.
"Nevada is, as we know, growing, and thus the most important places in the state to be sure that we get the National Seismic Hazard Model right are the growing urban areas," Anderson said. "For that reason, Rich Koehler (a geosciences assistant professor in the Nevada Bureau of Mines and Geology) and I took the lead in organizing the workshop to discuss what is known and, what are the most important things that we do not know. We expect that the results of the workshop will guide researchers to try to solve the most important problems in the next few years."
At the two-day workshop in 2018, dozens of geophysicists presented the latest information and research to update the seismic hazard maps for Nevada and eastern California. The workshop was a collaborative effort by the Nevada Seismological Lab and the Nevada Bureau of Mines and Geology.
Their paper, "A seismic hazards overview of the urban regions of Nevada: Recent advancements and research directions" was published June 5 online in the scientific journal Seismological Research Letters.
The 24 authors - geoscientists who specialize in geodesy, seismology, seismic network observations and seismic studies of earthquake ground motion - all provide information to the USGS for the National Seismic Hazard Model. Periodic updates of the National Seismic Hazard Model are subsequently adopted by the engineering community to set the design of buildings in this region, and throughout the nation.
"This information is valuable as we plan and expand our statewide seismic monitoring system," Seismo Lab Director Kent said.
The National Seismic Hazard Model is developed by the USGS as a community product through collaboration with researchers and engineers throughout the country. For Nevada and some of the adjacent parts of California, the University of Nevada, Reno provides key contributions to be sure that the NSHM is based on the best possible science.
The University has excellent programs that contribute to all of these research and outreach areas, specifically the Nevada Seismological Lab, The Nevada Geodetic Lab and the Bureau of Mines and Geology - all public service departments in the College of Science. This work is a part of the ongoing efforts of the Nevada Seismological Laboratory and Nevada Bureau of Mines and Geology to understand the seismic hazards of the state.
Earthquake preparedness information can be found on the Great Nevada Shakeout website and the Nevada Seismological Laboratory website.