Seismic Activity Increase in CA

Posted on August 12, 2020 by marcia

Earthquake swarm on San Andreas Fault beneath Salton Sea, California

Posted by Julie Celestial on August 12, 2020 at 18:02 UTC (3 hours ago)

A new earthquake swarm started beneath the Salton Sea in California on August 10, 2020. The risk of a larger earthquake over the next 7 days is considerably elevated due to the swarm when compared to background levels. The southernmost section of the San Andreas Fault is capable of rupturing in large magnitude earthquakes (M7+), the last of which occurred more than 300 years ago, USGS said.

The San Andreas Fault is considered as one of the most dangerous faults in the world. It stretches around 1 200 km (750 miles) and marks the boundary between the Pacific and North American tectonic plates. There are three major cities on the fault– Los Angeles, San Francisco, and San Diego, along with other towns.

The USGS has been monitoring an ongoing earthquake activity beneath the Salton Sea near the fault, with the largest quake recorded on August 10 as M4.6.

Image credit: TW/SAM, Google

This portion of San Andreas is capable of generating tremors of M7.0 and above. The last time an earthquake of this size hit the area was over 300 years ago.

“Historically, this area has seen swarms before– most recently in 2001, 2009, and 2016. During the last swarm in 2016, there were three bursts of activity separated by relatively quiet periods before the swarm ended,” USGS wrote.

“Past swarms in this area have remained active for 1 to 20 days, with a typical duration of about a week, so this swarm may have future bursts of activity that will in turn impact the probabilities discussed below.”

The agency warned that there are three possible scenarios of what could happen from August 12 to August 19.

The first scenario has a 98 percent chance of happening: earthquakes continue but will not be greater than M5.4 within the next week. The most likely scenario is that the rate of quakes in the swarm will decrease over the coming week.

Some moderately sized earthquakes may happen, within the range of M4.5 to M5.4. This may cause localized damage, especially in weak structures. Smaller earthquakes around M3.0 may be felt by people near the epicenters.

The second scenario has about a 2 percent chance of occurring: a larger earthquake could occur, ranging from M5.5 to 6.9. Earthquakes of this size may inflict damage around the Salton Sea area and may be followed by aftershocks that would increase the number of smaller quakes each day.

Scenario Three has less than 1 percent chance of taking place: a much bigger earthquake with M7.0 or higher could occur within the next seven days.

While the scenario has a very small probability, it would have major impacts on nearby communities if such a quake were to happen. It would be followed by aftershocks that would also increase the number of smaller shakes per day.

“No one can predict the exact time or place of any earthquake, including aftershocks or events in swarms. Our earthquake forecasts give us an understanding of the chances of having more earthquakes within a given time period in the affected area. We calculate this earthquake forecast using statistical analysis based on past earthquakes,” said USGS.

“We are carefully monitoring activity throughout the region and will continue to provide information to help people stay safe and care for themselves and each other.”

Featured image credit: USGS

from: https://watchers.news/2020/08/12/earthquake-earthquake-swarm-at-salton-sea-near-the-san-andreas-fault-california/

Movement at the San Andreas Fault

Posted on June 23, 2016 by marcia

Scientists discover a large-scale motion around San Andreas Fault

Posted by Seneca on June 21, 2016

A team of researchers from the University of Hawai’i at Mãnoa, University of Washington and Scripps Institution of Oceanography (SIO) analyzed the motion of Earth’s crust from the data collected by an array of GPS instruments placed near the San Andreas Fault System in Southern California. Their results revealed almost 201 km (125 miles) wide lobes of uplift and subsidence straddling the fault system. The motion has not been recorded so far, although it was predicted by theoretical models.

The GPS instruments record a vertical and horizontal motion of our planet’s surface. The tectonic motion of the crust, groundwater pumping, local surface geology, and precipitation amount all affect the vertical motion, and it was challenging to distinguish the broad, regional tectonic motion from the local motion.

The scientists have used comprehensive statistical methods to analyze the data recorded by the EarthScope Plate Boundary Observatory’s GPS network, and extract a large-scale pattern of smoothly varying vertical motions of the local crust.

San Andreas Fault in the Coachella Valley; from Keys View, February 12, 2014. Image credit: NPS/Robb Hannawacker/Joshua Tree National Park via Flickr-CC

“While the San Andreas GPS data has been publicly available for more than a decade, the vertical component of the measurements had largely been ignored in tectonic investigations because of difficulties in interpreting the noisy data. Using this technique, we were able to break down the noisy signals to isolate a simple vertical motion pattern that curiously straddled the San Andreas fault,” said Samuel Howell, a doctoral candidate at the UH Mānoa School of Ocean and Earth Science and Technology (SOEST) and lead author of the study.

The results responded to those previously predicted by an earthquake cycle model, led by co-authors Bridget Smith-Konter, associate professor at SOEST, and David Sandwell, a professor at SIO.

Uplift (red) and subsidence (blue) based on GPS data (top) confirm predicted motion (bottom). Image credit: University of Hawai’i

“We were surprised and thrilled when this statistical method produced a coherent velocity field similar to the one predicted by our physical earthquake cycle models. The powerful combination of a priori model predictions and a unique analysis of vertical GPS data led us to confirm that the buildup of century-long earthquake cycle forces within the crust are a dominant source of the observed vertical motion signal,” said Smith-Konter.

New research suggests the scientists can use GPS vertical motion measurements to improve the understanding of the structure and behavior of faults, even when no major ruptures occurred for decades or, even, centuries. Results are expected to contribute to constraining the seismic hazard estimates from the San Andreas Fault System, and could enable mapping of the large-scale motion resulting from the next significant rupture of the fault, in more detail.

Reference:

“The vertical fingerprint of earthquake cycle loading in southern California” – Samuel Howell, Bridget Smith-Konter, Neil Frazer, Xiaopeng Tong & David Sandwell – Nature Geoscience (2015) – doi:10.1038/ngeo2741

Featured image: San Andreas fault in the Coachella Valley; from Keys View, February 12, 2014. Image credit: NPS/Robb Hannawacker/Joshua Tree National Park via Flickr-CC

from: http://thewatchers.adorraeli.com/2016/06/21/scientists-discover-a-large-scale-motion-around-san-andreas-fault/

Tectonic Plate Movement Faster than Before

Posted on September 21, 2014 by marcia

Tectonic Plates Moving Faster: Study September 12, 2014

This aerial view of the San Andreas Fault shows how an untold number of slips have altered the landscape.

Scientists say they have found that Earth’s tectonic plates are now moving faster than at any other point in the last 2 billion years.Plate tectonics is the prevailing geologic process that shapes the planet.

It triggers most of the world’s strongest earthquakes and many volcanic eruptions, along with building mountains and moving continents.

While earlier research seemed to reveal that the massive tectonic plates are actually slowing down as Earth’s core cools, New Mexico Institute of Mining and Technology geochemist Kent Condie and colleagues say they have evidence of faster plate movements.

Writing in the journal Precambrian Research, the team says they looked at how often new mountain belts form when plates collide, and compared it to magnetic data from volcanic rocks.

That allowed them to determine where the rocks formed and how quickly the continents had moved.

Photo: U.S. Geological Survey

from: http://www.earthweek.com/2014/ew140912/ew140912a.html

Role of Salton Sea in Earthquake Abatement

Posted on July 9, 2011 by marcia

Study says Salton Sea is preventing large earthquakes

Published on July 2, 2011 12:45 pm PT
– By Dave Tole – Writer
– Article Editor and Approved – Warren Miller

(TheWeatherSpace.com) — A new scientific study, examining the fault structure of the southern San Andreas fault zone, has found that recent human regulation of the Colorado River may have delayed a major earthquake along the zone.

There hasn’t been a large earthquake under the Salton Sea for the past 300 years.

The study concludes that in the past, regular flooding of the Salton Sea area induced large earthquakes, occurring roughly every 180 years.

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