California Geological Survey Scientists Respond to Big SoCal Earthquakes

California Geological Survey scientists rushed to the Ridgecrest-Trona area after the July 4-5 earthquakes to gather data important to protecting public safety in the future.

A magnitude 6.4 earthquake occurred at 10:33 a.m. on the Fourth of July. There’s always a chance a larger earthquake will follow even an earthquake of that magnitude, and such was the case here: At 8:19 the following evening, a magnitude 7.1 quake struck.

Despite the concerns about ongoing seismic activity, getting scientific investigators on-site quickly was a priority.

Following large earthquakes, CGS focuses on finding evidence of seismic hazards as part of its regulatory mapping work. Like police detectives working on a crime, they hope for an undisturbed scene to gather clues.

Ground shaking causes most of the damage in a large earthquake. But there are other potentially damaging effects: surface fault rupture, landslides, and liquefaction (the ground behaving like quicksand). Examples of all three were found after these earthquakes.

Photo of DOC scientist with a ruler measuring the lateral displacement of surface rupture of the roadway caused by the Ridgecrest earthquake
CGS geologist Janis Hernandez takes lateral displacement measurements from roadway surface rupture.

CGS creates zones identifying where these hazards are known to exist or are likely to occur because of the geologic conditions. The zones require local governments to impose certain conditions when construction takes place to ensure public safety and minimize property loss. Of the hazards associated with earthquakes, surface fault rupture – breaks or cracks in the earth where one side of a fault has moved either vertically or laterally relative to the other side – is the easiest to avoid.  Assuming that you know where the rupture happens, that is.

California Geological Survey scientist Tim Dawson shows personnel from the Naval Air Weapons Station China Lake an example of fault rupture occurring on the base. USGS photo by Ken Hudnut

Evidence of surface fault rupture can be quickly lost because of weather or human activity, thus the urgency to get geologists to the scene. Roughly a dozen CGS scientists were either on the ground or above it, looking for ruptures from helicopters or utilizing drones equipped with high-resolution cameras.

In the video above, a CGS drone captures footage of surface rupture just south of Ransberg Road. The photo inset shows surface displacement on roadway in the area. The total measured right-lateral offset is about 6.5 feet and approximately 3 feet vertical. the large offset at bottom of photo is 5 feet.

Some CGS scientists were tasked with helping to organize the California Earthquake Clearinghouse. After a large quake, the Clearinghouse is established for government agencies, non-profit organizations, and academia. Typically set up with access to both the damaged area and the emergency operations field location, the Clearinghouse gives engineers, geologists, seismologists, sociologists, economists, and other researchers working in an earthquake’s aftermath a designated place to gather in order to share data and organize efforts.

Clearinghouse participants review, organize, and prioritize observations, then notify disaster responders and decision-makers at the Governor’s Office of Emergency Services State Operations Center in Sacramento about important information. For example, it was noted that surface fault rupture had offset a roadway between Ridgecrest and Trona under which water and gas pipelines ran. OES informed the utilities of that situation, prompting inspections and a water main repair.

Are you concerned about future earthquakes? CGS has created more than 500 “Alquist-Priolo” maps defining areas where surface fault rupture is a possible hazard, and more than 100 Seismic Hazard Zone maps for possible landslide and liquefaction hazards. You can use CGS EQ Zapp to see if your home is in a hazard zone.

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