On the early morning hours of April 30th, 2023, a moderate magnitude 4.5 earthquake
was felt throughout the Imperial valley in California, having been centered on the southeastern
edge of the Salton Sea.
However, this earthquake was centered one and a quarter miles east of a local active
volcano which few people know exist.
The complex I am referring to is the Salton Buttes volcano.
Having completely formed in the last 10,000 years, this small scale volcano contains magma
which actively exists at depth, probably around 3 miles depth in my opinion although we do
not know the exact depth of the present magma.
This molten rock actively vents gasses onto the surface, forming dozens of active fumaroles
and mud pots.
This magma even powers a local geothermal power plant, generating enough electricity
for several hundred thousand homes.
But, back to the earthquake which occurred, it was followed by 28 earthquakes in the next
5 hours, representing a true earthquake swarm.
This cluster consisted of 15 earthquakes large enough to be potentially felt, with 9 magnitude
2s, 3 magnitude 3s, and 3 magnitude 4 quakes.
Since these were clustered in close proximity to 4 of this volcano's 5 vents, you might
think that they are volcanic in origin.
However, fear not as these quakes were luckily not magmatic although they probably were volcanic
related.
` The Salton Buttes volcano is located in far
southern California on the southeastern edge of the Salton Sea, where it is 15.8 miles
north-northwest of the city of Brawley.
The Salton Buttes are the only land based volcano in the United States to be completely
below sea level.
As a whole, this complex could be best described as a lava dome complex, consisting of 5 rhyolite
lava domes which erupted in explosive eruptions between 5,800 BCE and 200 CE.
The vents are generally quite small, with lava not traveling any further than a half
mile.
The placement of these 5 vents on the shoreline is most likely sheer coincidence, as they
are parallel with a series of hidden faults in the Salton Sea itself.
The reason for the existence of this complex is that the Salton Sea is a small scale rift
zone of sorts.
To the north is the major San Andreas Fault and to the south is the Imperial Fault.
Inbetween these two faults, the crust is spreading apart to the southeast and northwest, allowing
for magma to intrude into the crust via a path of least resistance and occasionally
erupt onto the surface.``
While all of these 5 vents used to be distinct islands, the level of the Salton Sea has drastically
decreased over the last several decades due to a combination of less regional precipitation
and water overuse.
This declining water level has caused previously hidden geothermal features such as mud pots
and fumaroles to appear on land.
Due to the lake water and combination of ground water, hydrothermal fluids in the ground are
heated when they encounter rock overlying an active magma chamber.
This rock heats the water which carries volcanic gasses along with it, causing it to be pushed
upwards and reach the surface, but sometimes along the way encountering a fault line, causing
it to rupture and generate an earthquake.
The earthquake which occurred on April 30th was merely two orders of magnitude larger
than what is typical, with the aftershocks not representing additional hydrothermal activity
but rather stress release due to the aftershock itself.
This fact is best displayed via when the recorded aftershocks occurred in terms of the number
of minutes after the mainshock, which with the exception of another magnitude 4 earthquake
that triggered another aftershock sequence about an hour later, somewhat closely follows
the expected 1 over x rate of aftershocks.
In other words, for each minute after a mainshock earthquake, the chance of an aftershock decreases,
being around 1 over x with x representing the number of minutes which have passed.
As a whole, this earthquake sequence is likely to continue at a far weaker rate for the next
1 to 2 days and then will likely cease altogether.
This sequence was the strongest earthquake swarm to occur in 22 months at the Salton
Buttes, but earthquake swarms are quite common there due to its hydrothermal system.
Past stronger earthquake swarms with up to a magnitude 5.3 main quake have not resulted
in a volcanic eruption, and the same will almost certainly be the case with the current
situation, meaning a volcanic eruption is not about to occur.
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