(ETH) – A swarm of earthquakes that began southeast of the Salton Sea, in the Brawley seismic zone, that began on Sept. 30th, 2020. has produced a multitude of quakes since Wednesday with the swarm continuing today at a lower rate, with 4 magnitude 3 earthquakes recorded in the first 7 hours of Thursday, compared to 40 magnitude 3 and larger earthquakes recorded in the last 7 hours of Sept. 30th with the largest registering a magnitude 4.9 at 5:31 PM PDT on September 30th.
This particular region has produced swarms in the past –notably the 1981 Westmorland swarm, which produced a Magnitude 5.8 earthquake, and the 2012 Brawley swarm, which produced a Magnitude 5.4 quake. The USGS is stating that in a typical week,
there is approximately a 1 in 3000 chance of a magnitude 7+ earthquake in the vicinity of this swarm but has now reported three possible scenarios that we can expect from this current swarm in California and that one of these three scenarios will occur within the next week according to officials with the USGS. The following is from the USGS Website:
1. Scenario One (Most likely: 90%): Earthquakes continue, possibly including earthquakes up to magnitude 5.4.
The most likely scenario is that the rate of earthquakes in the swarm will decrease over the next 7 days. Some additional moderately sized earthquakes (M4.5 to 5.4) may occur, which could cause localized damage, particularly in weak structures. Smaller magnitude earthquakes (M3.0+) may be felt by people close to the epicenters.
2. Scenario Two (Less likely: 10%): A larger earthquake (magnitude 5.5 to 6.9) could occur within the next 7 days.
A less likely scenario is a somewhat larger earthquake could occur (up to a Magnitude 6.9). Earthquakes of this size could cause damage around the area close to the earthquakes that have already occurred and would be followed by aftershocks that would increase the number of smaller earthquakes per day. This scenario occurred in a previous swarm in the area – in 1981, when a swarm in this region included a magnitude 5.8 earthquake.
3. Scenario Three (Least Likely: approximately 1 in 300): A much larger earthquake (magnitude 7 or higher) could occur within the next 7 days.
A much less likely scenario, compared with the previous two scenarios, is that the ongoing swarm could trigger an earthquake significantly larger than the Magnitude 4.9 that occurred on the 30 September (i.e., Magnitude 7.0 and above). While this is a very small probability, if such an earthquake were to occur, it would have serious impacts on communities nearby and would be followed by aftershocks that would increase the number of smaller earthquakes per day.
