Last week’s 7.1 quake triggered fires, buckling part of a highway, damaging buildings but causing few reported injuries despite striking with eight times more force than the initial quake in the same area a day earlier. A statement issued by California Volcano Observatory (CALVO) said the seismic activity which started on Friday evening at the southern margin of the Coso Volcanic Field in Inyo County was continuing at a rate of 600 quakes a day with a magnitude of 1.0 or more. These had been triggered by a magnitude 5.4 earthquake at 9.19pm local time roughly 13 miles east south east of Little Lake, which was itself an aftershock of Friday’s more powerful tremor.
The statement said: “The intensity of the activity at Coso is gradually declining.
“Of the approximately 1,600 earthquakes detected at M1.0 or above since July 8, only 12 have been M3.0 or above, with the largest two registering M4.1.
“The current activity at Coso can be considered distant aftershocks, or triggered earthquakes.
“The M7.1 on July 5 occurred on a NW-trending fault oriented toward the Coso area, and it is common for large earthquakes to cause aftershocks beyond the actual fault rupture.
“No ground deformation indicative of volcanic activity has been detected, and there is no imminent threat of an eruption.
“The California Volcano Observatory will continue to monitor the situation for any sign of volcanic activity and provide updates as warranted.”
The Coso Volcanic Field is on the eastern side of the Sierra Nevada mountains at the northern end of the Mojave Desert, about 40 miles north of Ridgecrest.
The field covers roughly 150 square miles, mainly within the Naval Air Weapons Station at China Lake.
It is made up of lava domes, lava flows, and cinder cones erupted over the past 250,000 years.
The most recent eruption was about 40,000 years ago.
The United States Geological Survey’s National Threat Assessment, published in October, ranked the Coso Volcanic Field 72nd out of 161 US volcanoes with an overall score of 72.
Hawaii’s Kilauea, which erupted with devastating results last year, topped the list with a score of 263.
Another USGC report published last year, entitled California’s Exposure to Volcanic Hazards, warned: “The potential for damaging earthquakes, landslides, floods, tsunamis and wildfires is widely recognised in California.
“The same cannot be said for volcanic eruptions, even though they occur in the state about as frequently as the largest earthquakes on the San Andreas Fault.”
The report classifies the Coso Volcanic Field along with Mount Shasta, Medicine Lake volcano, Lassen Volcanic Centre, Clear Lake volcanic field, the Long Valley volcanic region, Ubehebe Craters and Salton Buttes as being located in a “land in a volcanic zone”.
Almost 200,000 people live, work or pass through one of these regions on a daily basis.
A report published last year published by the USGS along with scholars from the University of California and the University of Rhode Island suggested the Long Valley Caldera has a reservoir of semi-molten magma measuring 240 cubic MILES.