just in the past 24 hours there has been a big
earthquake swarm in Southern California with a magnitude 5.2 earthquake being the strongest a
whole bunch of magnitude fours and threes and everything else there's also been a magnitude 5.1
earthquake down here at the southern end of the San Andreas fault and so all of this is begging
the question are these for shocks for a big one to rupture in California so in this video we're
going to look at this earthquake swarm we're going to discuss what even is a big one we'll
look at the historic seismicity for California we'll also look at the stress accumulation rate
for the San Andreas and for California in general and much more hi everyone and welcome back to the
channel if you're new here my name is Stefan Burns let's Jump Right In in yesterday's video I talked
about how daily earthquake occurrence in global seismicity overall has dropped precipitously over
the past couple months you see that really nicely here the historic average for the 6 year time
frame is about 35 earthquakes per day magnitude 4 and greater now we're down to about 15 per day
magnitude 4 and greater so this is very bizarre if you haven't watched that video I recommend you
give it a watch to put this into greater context as it relates to our Earth and globalized miss
here we have our map for this earthquake swarm and also historic earthquakes for this area this is a
magnitude 5.2 earthquake in Lamont California the epicenter depth is 11.7 km so uh it's a crustal
earthquake and 5.2 is pretty strong there was also a whole bunch of magnitude fours and threes
and everything else below that and what's notable about this is that it was an earthquake swarm
whereas that 5.1 that was down in Mexico that I reference at the beginning of the video that
was just an isolated earthquake this is a whole swarm of them and it's in this interesting kind
of critical Junction Zone you have the San Andreas you have the Garlock fault here and then you have
all this Eastern seismicity and so this Garlock fault is accommodating a lot of plate motion over
off into the Sierra Nevada which is why the Sierra Nevada exists and we have that fairly close we
also have a lot of historic seismicity for this area most notably in 2019 there was a sequence of
earthquakes there was a 6.4 and then a 7.1 that occurred within 48 Hours of each other and you see
all the lower magnitude earthquakes that occurred after each one and so what you see is typically
you will have a strong earthquake and then all the aftershocks which are less in magnitude
but sometimes you get a strong earthquake it's actually a for shock and then the big earthquake
follows it's typically one magnitude stronger though often it can be even more than that so
is this a big earthquake precursor you could say right we have right now this trend of global
seismicity going down but now we get this big earthquake swarm along and right next to the San
Andreas and Garlock fault and this this plate area hasn't really accommodated and released a lot of
the stress that's been building up and so a lot of people may be asking is this a foreshock for
the big one but to answer that question we have to first understand what is the big one there's
no single definition for what is a big one but we do have three earthquakes here that are very
notable for California estimated magnitude 9 and 1700 this is the Cascadia Earth earthquake so it
happened Northern California that Cascadia Zone and then the two that most people know of are
the magnitude 7.9 this is the 1857 great Fort ton earthquake and then the magnitude 7.8 1906
great San Francisco earthquake that also had the fire which made it especially destructive and
so all three of these are big ones this one 1857 was really significantly felt and recorded and
logged and it's kind of an example of how you can have very strong powerful earthquakes in Southern
California and now with Southern California being so industrialized and so many people living there
if something like the great Fort ton earthquake occurred it could be very destructive a lot of
lives loss Etc so that is also like a example of a great earthquake and so just some scale ratings
to keep in mind a magnitude 8 earthquake is about three times bigger and 5.6 times strong stronger
than a magnitude 7.5 so it might not seem like much of a difference going from 7.5 to 8 but 5.6
times stronger and then a magnitude 9 earthquake is 16 times bigger and 63 times stronger than a
magnitude 7.8 so this Cascadia earthquake was 63 times stronger than the great San Francisco
earthquake and so we don't have to worry in Southern California or in the North Bay Area
like San Francisco about a Cascadia earthquake the estimates from the USGS show that the San
Andreas fall can probably accommodate at maximum a magnitude 8 earthquake that's what we see in
the historic record that's what we see right here 7.9 and 7.8 and so once you start getting close to
magnitude 8 then you're in that big one territory this magnitude 5.2 earthquake in the earthquake
swarm that occurred is quite significant but if we put it into context we see that's it's not
really that big of a deal and so here we see 2.5 to 5.4 magnitude earthquakes they're often
felt but they typically only cause very minor damage to buildings it's only once you get into
that 5.5 to six range that you start to cause damage to buildings though it's still just slight
it's when you get to six seven and eight that you can really get destructive earthquakes for example
the South Napa earthquake was a magnitude six that cause over a billion dollars worth of damage
in Napa uh and then if you go up into seven you have major earthquakes causing serious
damage in a magnitude a can cause complete destruction near its epicenter depending on
the type of infrastructure depending on the geology its sheer wave characteristics and the
resonant frequencies of that the actual frequency distribution of the earthquake that's getting a
little bit more complex but it all matters and so if you're building on top of loose sediment it's
going to be much different than you're on Bedrock Bedrock will allow those waves to pass through and
jolt through really quickly whereas loose sediment can kind of amplify the waves and with the South
Napa earthquake magnitude 6 it's basically in the Napa Caldera and it caused this resonance to
occur because the waves kept bouncing back and amplifying here we have historic California
earthquakes 1769 to 2000 these big circles there are for magnitude seven and greater
earthquakes and so we see a cluster there in the North Bay across different time frames
the colors are for the different dates red is the oldest green is the newest we see a whole
bunch here in the Cascadia region we also see some blank zones that don't get much earthquake
activity and then you see these magnitude sevens and also lesser magnitude earthquakes kind of
spread out around Southern California so quite a lot of magnitude 7 and greater earthquakes have
occurred just since uh the 1700s and we had those the 7.1 that occurred in 2019 just nearby kind of
in this Zone here and so these do occur magnitude 5.2 put into context of a magnitude 7even or
greater is again very very weak but it brings this back into people's Consciousness the fact
that earthquakes exist because all of a sudden now you feel the ground shaking it doesn't
cause much serious damage or harm but it's a very visceral reminder that California is a very
earthquake prone state that's very geologically active and it does host the potential for big ones
magnitude 7.5 magnitude 8 and then an up in this region even greater potentially up into magnitude
8.5 and magnitude 9 that that' be more up in like the Washington subduction zone area here we have
a fantastic graphic showing the strain rate for parts of the San Andreas fall and for other fall
systems in California we see our Legend here this is for the strain rate nanostrain per year we see
its orders of magnitude there so it goes from one to a thousand and we see that there's plenty
of places where there's very low strain rate but then right along the main fault systems that
strain rate spikes so if I step off here we can see the full graphic we see that there's quite
a high strain rate in the San Francisco be area region and also going south and then that strain
rate decreases this is where there's a creeping segment and there's more seismicity in general but
it's being released through low grade activity and there's more slip being accommodated so the strain
rate is less overall and then we get these lock sections like down here by San Diego and down into
Mexico where the strain rate is quite high and as that accumulates as that stress accumulates you
have greater and greater and greater potential for a big one especially if you haven't had a
lot of earthquake activity recently remember keep in mind the the way earthquakes scale is that
they scale very fast and so we talked about how a magnitude 9 earthquake is 63 times stronger than
magnitude 7.8 right a magnitude 5 earthquake in a swarm is definitely releasing energy but it's
not releasing that much energy in context of a magnitude 7.5 earthquake or magnitude 8 earthquake
and so there could be a slight release of tension on a fault because of a magnitude 5 and swarm
but not that much it may not delay uh a big one for that long you could say and it could even be
a sign that things are now becoming more active and waking up and so we see that the strain rate
changes across the San Andreas fault these are the areas where the earthquake risk is the highest
and that you have the biggest potential basically for a big one and we also see that it depends on
your location to the fault so we see that here you have some velocity on these plates right this
is our cross line there you have some velocity on these plates but then right at that fault the
velocity and the slip goes to zero and that's why that strain spikes up so much so the San
Andreas in general SoCal is very much in red risky territory for a big one for the next 30
Years according to the USGS also San Francisco but up in the Bay Area they're really looking at
the Hayward fault as being a very risky fault Zone that can host a very large earthquake magnitude
seven or greater because it hasn't ruptured in a while and there's such a dense amount of people in
infrastructure over the Hayward fault region we'll wrap up by looking at our earthquake hazards map
for the United States here is our Legend burgundy is highest Hazard white is lowest Hazard if we
look at Alaska we see that's all very high Hazard along the coast because of the subduction zone
the ring of fire there this can have very large earthquakes magnitude nine we've seen that before
historically Hawaii the big island is high Hazard because of the shield volcano we see New Madrid
fault Zone some other little areas there of higher Hazard but they don't slip that often uh they
have the potential for large earthquakes but the real zone of high earthquake hazard for the United
States is this western coast so we have California going through Oregon and then Washington here you
can have subduction earthquakes and here it's more uh transformed fault earthquake so the highest
magnitude that you can probably have in California is about magnitude 8 and then up here you start
to go into the 8 plus range even up into nine really there because you have some significant
subduction occurring off the coast of Washington Canada and then into Alaska and so the United
States in general is a pretty active area seismically if we look at the West Coast we see
this also going off into like the Sierra Nevada and then even further into uh the interior of the
Continental us and then we have the New Madrid but there are areas of low earthquake risk and so
with a magnitude 5.2 earthquake in California perhaps the foreshock it's more likely to be
an isolated event for shocks uh are quite rare in terms of it being a significant foreshock and
then an even bigger earthquake that follows but it does occur it's about 10% of the time uh and
we're seeing a lot of earthquake activity now in Texas because of all the oil and gas drilling
in the fracking that's occurring there and so that whole area is being basically punctured
and fractured and that's causing an increase in seismicity for Texas it's like swiss cheese
down there basically and so we're seeing a lot of big earthquakes now out of Texas magnitude 4
some of them even greater and so that's an area that they're going to probably have to update this
map to show increase earthquake hazard as a result but again magnitude 5 earthquakes you'll feel
them but they really don't cause that much damage so when we're looking at this highest Hazard
we're looking at magnitude eight earthquakes along California as being basically the upper part
of that scale rating and then magnitude eight and greater as we move up from Northern California
through Washington and into Canada and Alaska so thanks so much for watching the video I hope you
found that useful I'll will keep you up to date with what is happening I recommend you watch my
video I made yesterday on global seismicity why it's been decreasing we don't exactly know why and
when that's going to rebound perhaps The Rebound in global seismicity will be what triggers a big
one who knows we don't know so you can watch that video here and click the thumbs up help this
channel grow subscribe if you like to see more content like this I've been your host Stefan
Burns thank you so much and have a great day