Magnitude 5.2 Earthquake in Mono County, California.

The United States Geological Survey recorded a Magnitude 5.2 Earthquake at a depth of about 8.8 km roughly 30 km to the southeast of the town of Bodie in Mono County, California, slightly after 7.35 am local time (slightly after 2.35 pm GMT) on Saturday 11 April 2020. There are no reports of any damage or injuries relating to this quake, but people have reported feeling it across much of northern California, southern Oregon. and western Nevada.

The approximate location of the 11 April 2020 Mono County Earthquake. USGS.

California is extremely prone to Earthquakes due to the presence of the San Andreas Fault, a tectonic plate margin that effectively bisects the state. The west of California, including Santa Barbara and Los Angeles, is located on the Pacific Plate, and is moving to the northwest. The east of California, including Fresno and Bakersfield is on the North American Plate, and is moving to the southeast. The plates do not move smoothly past one-another, but constantly stick together then break apart as the pressure builds up. This has led to a network of smaller faults that criss-cross the state, so that Earthquakes can effectively occur anywhere.

Tectonic boundaries and faults in California and the surrounding area. USGS.

Witness accounts of Earthquakes can help geologists to understand these events and the underlying structures that cause them. If you felt this quake (or if you were in the area but did not, which is also useful information) then you can report it to the United States Geological Survey here.

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Rockfall kills two climbers in the Sierra Nevada mountains of California.

The bodies of two climbers missing since Sunday 27 October 2019 were recovered from Red Slate Mountain, in the Sierra Nevada range of California, on Wednesday 30 October. Friends notified Mono County Search and Rescue when Jennifer Shedden, 34, of Mammoth Lakes, and Michelle Xue, 22, of Los Angeles, failed to return from a climbing trip on the mountain. The bodies of the two women were sighted in the in a couloir (narrow, steep-sided gully) on Monday by a California Highway Patrol helicopter. They were still attached to the rockface by ropes, and had apparently been killed by a rockfall, although rescuers were unable to recover them due to continuing instability on the rockface, with a second attempt by the National Guard failing the next day. The bodies were eventually retrieved by a Yosemite Search and Rescue helicopter. Both women are described as having been highly experienced climbers, and well equipped for the expedition.

A rescue team on Red Slate Mountain following the deaths of two climbers this week. Mono County Sheriff's Office.

Red Slate Mountain forms part of the Sierra Crest, a ridgeline that runs 800 km north-to-south through the Sierra Nevada Mountains, slightly to the south of the Long Valley Caldera. The mountain is not actually made of slate, but rather hornfels and marble, forms of mudstone and limestone that have been metamorphosed by heating and pressure. The area is seismically active; mountains appear to be permanent structures to humans, but are actually dynamic active systems, being constantly uplifted (in the case of the Sierra Nevada by the subduction of the last chunks of the ancient Farallon Plate along the Pacific Coast of North America), and constantly worn down by erosion, with the area around the Long Valley Caldera being particularly prone to movements. This combination of regular rock movements and a strong seasonal freeze-thaw cycle makes the area particularly prone to rockfalls (heating and cooling of the rock on a seasonal, or even daily, cycle, causes the minerals to expand at different rates, leading to the formation of cracks).

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Magnitude 4.0 Earthquake in Mono County, California.

The United States Geological Survey recorded a Magnitude 4.0 Earthquake at a depth of 7.7 km in northern Mono County, California, slightly before 0.50 am local time (slightly before 7.50 am GMT) on Friday 30 May 2014. There are no reports of any damage or casualties associated with this event, though it was reportedly felt up to 200 km away.

The approximate location of the 30 May 2014 Mono County Earthquake. Google Maps.

California is extremely prone to Earthquakes due to the presence of the San Andreas Fault, a tectonic plate margin that effectively bisects the state. The west of California, including Santa Barbara and Los Angeles, is located on the Pacific Plate, and is moving to the northwest. The east of California, including Fresno and Bakersfield is on the North American Plate, and is moving to the southeast. The plates do not move smoothly past one-another, but constantly stick together then break apart as the pressure builds up. This has led to a network of smaller faults that criss-cross the state, so that Earthquakes can effectively occur anywhere.

Witness accounts of Earthquakes can help geologists to understand these events and the underlying structures that cause them. If you felt this quake (or if you were in the area but did not, which is also useful information) then you can report it to the United States Geological Survey here.

See also...

 Magnitude 3.8 Earthquake in Mineral County, Nevada.

The United States Geological Survey recorded a Magnitude 3.8...



 Magnitude 3.6 Earthquake in Inyo County, northern California.

A Magnitude 3.6 Earthquake at a depth of 12.8 km occurred close to...

 Northeast California shaken by Magnitude 5.7 Earthquake.

A Magnitude 5.7 Earthquake struck northeastern California on...


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