The Pacific Tsunami Warning Center's Response to the Intensive Earthquake Sequence South of Puerto Rico in January 2020

Session: Early Results from the 2020 M6.4 Indios, Puerto Rico Earthquake Sequence
Type: Oral
Date: 4/30/2020
Time: 09:15 AM
Room: 115
Description: 

Historically, the Pacific Tsunami Warning Center has issued tsunami messages for earthquakes in the Puerto Rico seismic region at a rate of 3 to 12 messages per year. The occurrence of a magnitude 5.7 earthquake offshore southwestern Puerto Rico on 6 January 2020, however, marked the onset of an intense earthquake sequence leading to the occurrence of the larger 6.4 magnitude earthquake on 7 January 2020. PTWC's preliminary local ML magnitudes estimates of 5.7 and 6.6 for the two largest earthquakes of this seismic sequence allowed the issuance of official tsunami messages within 04:39 and 05:11 minutes from origin time. Typically, the system processes fewer than an event per hour. Since 6 January 2020, however, the PTWC automatic seismic processing system for Puerto Rico and the Virgin Islands detected and processed more than 15 earthquakes of magnitude greater than about 2.0 per hour, peaking at a maximum of 393 earthquakes per day on January 8, 2020. This dramatic increase in seismic activity, marked by the occurrence of a very large number of aftershocks with magnitudes larger than 4.0, required operational adjustments, including several temporary modifications of the procedures for Puerto Rico: a) raising from 4.0 to 4.5 the magnitude threshold to send official tsunami messages, b) sending observatory messages for events with preliminary ML magnitudes larger than 4.0 but smaller than 4.5 and c) increasing from 3.5 to 3.9 the automatic magnitude threshold to page the scientists on duty. Between 6 and 12 January 2020, the PTWC had sent 72 observatory messages and 31 tsunami information statements with a median response time of 3 m and 40 s from origin. Despite the stress on the PTWC systems and its already reduced scientific staff, within a week the PTWC had issued 103 messages for earthquakes with magnitudes larger than about 4.0, double the number of messages sent in the previous 9 years combined.

Presenting Author: Victor Sardina

Authors