M7.1 Ridgecrest Earthquake - USGS Aftershock Forecast

M7.1 Ridgecrest Earthquake - USGS Aftershock Forecast

The USGS has issued its Aftershock Forecast following M7.1 Ridgecrest, CA earthquake at 03:19 UTC on July 6, 2019. An updated version issued 02:55 UTC, July 7 is posted below and marked Update.

Over the next 1 week, there is is a 3 % chance of one or more aftershocks that are larger than magnitude 7.1. 

It is likely that there will be smaller earthquakes over the next 1 Week, with 240 to 410 magnitude 3 or higher aftershocks.

Magnitude 3 and above are large enough to be felt near the epicenter.

The number of aftershocks will drop off over time, but a large aftershock can increase the numbers again, temporarily.

Image credit: Google, TW. Data source: USGS (July 5-6, 2019)

The USGS estimates the chance of more aftershocks as follows:

Within the next 1 week ending 15:00 UTC July 13, 2019:

  • The chance of an earthquake of magnitude 3 or higher is > 99 %, and it is most likely that as few as 240 or as many as 410 such earthquakes may occur in the case that the sequence is re-invigorated by a larger aftershock.

  • The chance of an earthquake of magnitude 5 or higher is 96 %, and it is most likely that as few as 0 or as many as 8 such earthquakes may occur.

  • The chance of an earthquake of magnitude 6 or higher is 27 %, and it is most likely that as few as 0 or as many as 2 such earthquakes may occur.

  • The chance of an earthquake of magnitude 7 or higher is 3 %, such an earthquake is possible but with a low probability.

"Due to the very high rate of earthquakes in the earliest part of the sequence, we are not able to count all events," the agency said.

So far in this sequence, there have been 233 M3 or higher earthquakes, which are strong enough to be felt, and 4 M5 or higher earthquakes, which are large enough to do damage.

Be ready for more earthquakes

  • More earthquakes than usual (called aftershocks) will continue to occur near the mainshock.
  • When there are more earthquakes, the chance of a large earthquake is greater which means that the chance of damage is greater.
  • The USGS advises everyone to be aware of the possibility of aftershocks, especially when in or around vulnerable structures such as unreinforced masonry buildings.
  • This earthquake could be part of a sequence. An earthquake sequence may have larger and potentially damaging earthquakes in the future, so remember to: Drop, Cover, and Hold on.

Update

Aftershock Forecast update issued 02:55 UTC, July 7:

What we think will happen next

According to our forecast, over the next 1 Week there is a < 1 % chance of one or more aftershocks that are larger than magnitude 7.1. It is likely that there will be smaller earthquakes over the next 1 Week, with 79 to 190 magnitude 3 or higher aftershocks. Magnitude 3 and above are large enough to be felt near the epicenter. The number of aftershocks will drop off over time, but a large aftershock can increase the numbers again, temporarily.

More details about the earthquake forecast are provided in the section “Our detailed aftershock forecast” below.

About this earthquake and related aftershocks

The expected numbers and probabilities of aftershocks have gone down since the previous forecasts for two reasons. First, it is due to the natural and expected decrease in activity as time passes since the mainshock. Second, our observations of this aftershock sequence show that the activity is decreasing slightly more quickly than average for this area. We have adjusted the forecast to account for both factors.

So far in this sequence there have been 297 magnitude 3 or higher earthquakes, which are strong enough to be felt, and 4 magnitude 5 or higher earthquakes, which are large enough to do damage.

Our detailed aftershock forecast

The USGS estimates the chance of more aftershocks as follows: Within the next 1 Week until 2019-07-14 02:50:00 (UTC):

  • The chance of an earthquake of magnitude 3 or higher is > 99 %, and it is most likely that as few as 79 or as many as 190 such earthquakes may occur in the case that the sequence is re-invigorated by a larger aftershock.
  • The chance of an earthquake of magnitude 5 or higher is 71 %, and it is most likely that as few as 0 or as many as 5 such earthquakes may occur.
  • The chance of an earthquake of magnitude 6 or higher is 12 %, and it is most likely that as few as 0 or as many as 2 such earthquakes may occur.
  • The chance of an earthquake of magnitude 7 or higher is 1 %, such an earthquake is possible but with a low probability.

Source

Featured image credit: Google, TW. Data source USGS (July 5 - 6, 2019)


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