Is this M5.2 SoCal Earthquake Swarm a Foreshock to a "Big One"?

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