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Evening Update - Thursday, January 16, 2020

January 16, 2020

Earthquake Aftershock Forecast and Scenarios

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2020 Puerto Rico Earthquake SequenceEarthquakes detected between December 28, 2019 as of January 16, 2020. Subject to updates (Public domain.)

7-Day Aftershock Forecast

The USGS aftershock forecast indicates there is a 3 percent chance of a magnitude 6.4 or larger aftershock over the next 7 days.

30-Day Aftershock Scenarios

Based on our aftershock forecasts, USGS has modeled three possible scenarios for this earthquake sequence as it evolves over the next month. These scenarios represent what could happen from January 17 to February 17, 2020. Only one of these scenarios will occur. The earthquakes in these scenarios would occur in the areas near where aftershocks are happening now. Regardless of scenario, earthquakes will continue to occur for days, months, or potentially years to come. It is very unlikely the aftershocks will cease completely within the next month.

Scenario One (most likely): 79 percent chance [same as yesterday]

The most likely scenario is that aftershocks will continue to decrease in frequency over the next 30 days, with no further earthquakes similarly sized to the M 6.4 that occurred on Jan. 7, 2020 (i.e., will be less than M 6.0). Some of these moderately sized aftershocks (M 5.0+) may cause localized damage, particularly in weak structures. Smaller magnitude earthquakes (M 3.0+), when at shallow depth, may be felt by people close to the epicenters.

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Secuencia del Terremoto en Puerto Rico, 2020Terremotos detectados entre diciembre 28, 2019 hasta enero 16, 2020. Sujeto a actualizaciones. (Public domain.)

Scenario Two (less likely): 18 percent chance [same as yesterday]

A less likely scenario is an earthquake occurring of similar size as the M 6.4 event. This is called a “doublet”: when two large earthquakes of similar size occur closely in time and location. This earthquake could cause additional damage in the same region and increases the number of aftershocks.

Scenario Three (least likely):  3 percent chance [same as yesterday]

A much less likely scenario than the previous two scenarios is that recent earthquakes could trigger an earthquake significantly larger than the M 6.4 that occurred Jan. 7, 2020 (i.e., M 7.0 and above). While this is a small probability, if such an earthquake were to occur, it would have serious impacts on communities nearby. This sized earthquake would also trigger its own aftershock sequence, so the rate of small and moderate earthquakes would increase again.

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