Assessment of the Aftershock Probability Estimates of the 2019–2020 Southwestern Puerto Rico Earthquake Sequence

Session: Early Results from the 2020 M6.4 Indios, Puerto Rico Earthquake Sequence [Poster]
Type: Poster
Date: 4/30/2020
Time: 08:00 AM
Room: Ballroom
Description: 

Estimates of aftershock decay after a main event are useful for information dissemination in areas where the population has experienced a catastrophic event and as a result are in constant anxiety of what to expect. The method of Reasenberg and Jones (1989,1994) has proven accurate for segments of the San Andreas fault in California (Hardebeck et al., 2018) and by using Garcia et al. (2012) tectonic regionalization, Page et al. (2018) was able to apply aftershock production and decay rates to seismic clusters globally. The Northern Caribbean Plate Boundary Zone features as a Stable Oceanic Region in the classification of Garcia et al. (2012). In this study we use the parameters employed to describe the production of aftershocks in selected events within the seismic sequence of southwestern Puerto Rico that began on December 29, 2019 with a M4.7 event. We compare the observed aftershock production to the estimates predicted by the equations and evaluate the change in parameters necessary to adjust a decay rate in agreement with observed data. We also look at the probabilities of triggering variable magnitude events in the sequence and compare to the observed outcome. Aftershock predictions published by the USGS placed only one percent chance of having a larger than M5.0 magnitude event when the Mw5.0 January 6, 2020 occurred. However, 22 hours later, a Mw6.4 event occurred kilometers from the previous event, thus questioning the estimates and the parameters employed for the region. Unfortunately, the completeness of the catalog for the current location has suffered from exhaustion on Puerto Rico Seismic Network analysts, as felt events and alarms are priority in the location process, hence the smaller microearthquakes have been relegated to a lower priority. Recalling that aftershock probabilities are independent of number of faults, discrepancies in the model predictions may be the results of multiple segments triggered by stress transfer, in which case, models would require modifications.

Presenting Author: Alberto M. Lopez

Authors