Thread by @drrocks1982

THREAD: Regarding the #RidgeCrestearthquake and #Coso #volcano there has been a lot of concern, mostly from misinformation broadcast by non-geologists, that the #earthquake sequence near #Ridgecrest, CA means an imminent eruption from the Coso Volcanic Field or was caused by it.

Coso is directly tied to the subject I was working on for my Ph.D. (geo.arizona.edu/Antevs/Theses/…), so I spent a lot of time getting to know it and its neighboring volcanoes and faults.

The following is a summary of what geoscientists know about Coso, how it is monitored, and what we can realistically expect from it. If this is at all useful to you, please feel free to share it.

Coso is indeed a volcanic system, currently dormant. It is a mishmash of cinder cones, volcanic domes, and lava flows, which is consistent with the style of young volcanoes that appear east of the Sierra Nevada extending northward towards the border with Nevada.

These volcanoes exist because this part of the North American continent has been stretched out by various tectonic forces over the last 20 million years. Tanya Atwater's famous plate tectonic reconstruction shows this ().

I used earthquakes to map the structure and infer the composition of the crust and upper mantle across this region as much as possible: pubs.geoscienceworld.org/gsa/geosphere/….

Because of this work and other studies before/after, we know that the crust is only 25-30 km thick in eastern California, which means that during the process of stretching, rock in the mantle gets much closer to the surface than it normally would.

The uppermost mantle in southwestern North America is very hot (>1200 °C), so as it rises and decompresses, small amounts reach the pressure-temperature conditions needed to begin melting. e.g. agupubs.onlinelibrary.wiley.com/doi/full/10.10…, agupubs.onlinelibrary.wiley.com/doi/pdf/10.100…

This magma (basalt, like what you see in Hawaii) accumulates in certain areas (perhaps due to the temp. or composition of the starter mantle rock) and can find pathways (fractures, faults) to leak upward through the stretched crust lying above it.

When this magma reaches the surface, it usually forms these little volcanic fields, mostly comprised of one-and-done cinder cones, lava flows, maars, etc. that you can pick out on satellite images because of sparse vegetation and low erosion rates. See Big Pine and Coso below.

If there's a lot of melt, it can linger in the crust and distill itself into a more silica-rich and explosive magma. This results in repeated, larger eruptions, making volcanic systems with bigger footprints. Long Valley Caldera is a prime example of this. volcanoes.usgs.gov/volcanoes/long…

This animation provides some background on different styles of eruptions in the Basin and Range, which Coso and other eastern California volcanoes reside within:

Because of its role as a geothermal power producer, there's been some interesting science done to image what Coso volcanic system looks at depth. This paper provides an example of these studies: pdfs.semanticscholar.org/058d/f600a76c1…

You can read in detail and find additional references about Coso's eruptive history here:
volcanoes.usgs.gov/volcanoes/coso…, volcano.si.edu/volcano.cfm?vn…

The @USGS evaluated Coso as a moderate hazard (pubs.usgs.gov/sir/2018/5140/…), meaning it must be monitored. It has been observed with modern geophysical instruments since the mid-1990s, including seismic & geodetic stations operated by @CalTech, @usgs_seismic, @IRIS_EPO, @UNAVCO, etc.

These data are freely open to the public for analysis. Because of this bounty, seismologists and geodesists can detect even tiny earthquakes throughout the entire volcanic system and watch the movement of the Earth's surface which may result from magma moving at depth.

You can see the closest seismic stations here: ds.iris.edu/gmap/#network=…
and an example of data from the nearest geodetic sensor here: geodesy.unr.edu/NGLStationPage…
unavco.org/data/gps-gnss/…

As the USGS notes on its Coso page, there was a swarm of earthquakes that began after one of the larger Ridgecrest aftershocks. volcanoes.usgs.gov/volcanoes/coso…

From their catalog, you can see the fault(s) that were activated by the main event and aftershocks, and then the separate set of earthquakes stimulated around the Coso Volcanic Field to the northwest of those faults.

This is not abnormal! Large earthquakes release a lot of energy (in the case of the M7.1, ~3000 Little Boy atomic bombs), and that and its many aftershocks were right next door geologically speaking.

These jostled the relatively small (a few % of total volume) amounts of melt, superheated fluids, and gases that reside within the crust under Coso. In areas like this, it is very normal to see swarms of smaller quakes or tremor as the material finds a new equilibrium.

But, there is no evidence yet of an eruption on the way. For starters, this is an extremely seismically active area. From 1970 until July 1st, there were 172 earthquakes over M5 in the general region of Coso (ds.iris.edu/ieb/index.html…

In 1872, just up US-395 near Lone Pine, there was a high M7 (pubs.er.usgs.gov/publication/70…) earthquake which produced a fault scarp that you can still see today (with yours truly, post fieldwork circa 2007).

Knowledge of the how this region deforms from fault slip histories and GPS data (and basic logic) allows us to infer that Coso has been shaken from all sides by large earthquakes since its last activity 10,000 to 40,000 years ago.

Seismologists and volcanologists generally regard volcanoes that get knocked into eruption (a very rare event) by large nearby earthquakes to already be very close to their tipping point, and before this event Coso was quiet.

When an eruption does finally occur at Coso, there is fortunately very little infrastructure (aside from the geothermal powerplant and U.S. Navy presence) or population in the area.

Moreover, the eruptive history tells us that the area impacted is likely to be small relative to most of the more recognized volcanoes in the western U.S.

In summation, it is a statistical certainty that Coso will erupt again, but unless specific indicators of volcanic activity manifest (all of which are plainly recognizable to the scientists tasked with its monitoring) then it's not likely to be because of this earthquake.

So, anyone who says Coso either caused the M6.4/7.1 or is about to erupt is is not playing with a full deck when it comes to how the Earth works in this region.

It also opens a more philosophical debate on how we process risk and why the siren call of YouTube experts is answered by so many, but that is a thread for another day.

P.S. Major shoutout to the colleagues who dropped everything to survey the fault in blistering summer heat, deploy more instruments to record aftershocks, crank through the initial data to understand this EQ and future hazard, and communicate with countless concerned people.