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Session: The 7 January 2020 South of Indios (M6.4) Earthquake in Puerto Rico, Response and Lessons

Type: Oral

Date: 4/22/2021

Time: 02:30 PM

Time: Room 3

Description: The 7 January 2020 South of Indios (M6.4) Earthquake in Puerto Rico, Response and Lessons

A sequence of earthquakes offshore Guayanilla and Guánica, Puerto Rico, began in December 2019 and continues as of January 2021. The USGS began issuing Operational Aftershock Forecasts for this sequence after the first M5.0 event occurred on 29 December. Initial forecasts used the Reasenberg and Jones (RJ89) model (Science, 1989) as updated in Page et al. (BSSA, 2016). That model ties all aftershocks to the mainshock and so the forecasts for the 29 December event were superseded when a M5.8 earthquake occurred on 6 January. And that forecast was superseded when an M6.4 event occurred the next day. The forecast was updated throughout 2020 and into 2021. After an M5.9 aftershock on 11 January, the RJ89 model did not sufficiently capture the complexity of the sequence, and we began using an Epidemic Type Aftershock Sequence model (Ogata, JAmStat, 1988). Although the initial sequence displayed some swarm-like features (elevated background rate), the post-mainshock sequence appears to be dominated by inter-event triggering. The sequence has maintained rigorous productivity, consistent with the forecast.

Our standard aftershock forecasts are presented on the USGS earthquake event pages and contain text commentary and a table of expected numbers of events and probabilities. To help people interpret the probabilities, we developed a set of three aftershock sequence scenarios based on experience from past sequences in New Zealand. The scenarios were released via the USGS web site in English and Spanish. To support FEMA and local government decisions, an Open-File report on the expected duration of the sequence was released. Further research is being conducted regarding product testing, engaging with key stakeholders and publics within Puerto Rico. This research, led by the University of Puerto Rico and funded by the Natural Hazards Center, aims to inform the development of the forecast template 2.0, including visualizations to express the forecast better.

Presenting Author: Nicholas van der Elst

Additional Authors

Nicholas van der Elst

Presenting Author Corresponding Author

nvanderelst@usgs.gov

U.S. Geological Survey, Pasadena, California, United States

Michael Barall

mbarall@contractor.usgs.gov

Invisible Software, Mountain View, California, United States

Jeanne L Hardebeck

jhardebeck@usgs.gov

U.S. Geological Survey, Mountain View, California, United States

Andrea L Llenos

allenos@usgs.gov

U.S. Geological Survey, Golden, Colorado, United States

Eric Martinez

emartinez@usgs.gov

U.S. Geological Survey, Golden, Colorado, United States

Sara K McBride

skmcbride@usgs.gov

U.S. Geological Survey, Mountain View, California, United States

Andrew Michael

ajmichael@usgs.gov

U.S. Geological Survey, Mountain View, California, United States

Morgan T Page

mpage@usgs.gov

U.S. Geological Survey, Pasadena, California, United States

Jenniffer Santos-Hernández

jenniffer.santos1@upr.edu

University of Puerto Rico, Rio Piedras, Puerto Rico, United States Territories and Minor Outlying Islands

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