Post-Seismic Offsets in Southwestern Puerto Rico After the M6.4 7 January 2020

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: 

Microseismic activity in Southwestern Puerto Rico (SWPR) within the Puerto Rico and Virgin Island (PRVI) block in northeastern Caribbean, has drawn attention to recently recognized North Boqueron Bay-Punta Montalva Fault Zone (NBB-PMFZ; Roig et al., 2013 and Adames, 2017). The recent seismic sequence seems to have initiated on a southeast offshore extension of the NBB-PMFZ starting with a Ml 4.7 event on December 28, 2019 and producing several M5 precursory and aftershock events. The main shock of Mw 6.4 on January 07, 2020 could be the result of stress transfer from the offshore NBB-PMFZ to a northeast-trending normal fault, possibly the Guayanilla Canyon fault. The focal mechanism computed by USGS NEIC was used to predict co-seismic offsets at nearby GPS stations. For the last two decades, GPS data has been collected throughout the PRVI block (Jansma et al., 2000, Jansma and Mattioli, 2005; Ihemedu, 2011; Solares, 2019) to quantify its kinematics. Results from last epoch showed that the SWPR block behaves separately from the rest of the PRVI block (Solares, 2019). A new epoch of GPS measurements has initiated after the main schock. All GPS data from campaing and continuous sites will be processed with GIPSY-OASIS II (v.6.4) using precise point positioning and final products in IGS14 to compare the predicted offsets to observed post-seismic deformation at GPS sites. TDEFNODE will be used with a grid-search strategy to find the best-fitting elastic half-space parameters that minimize the errors relative to observed coseismic (and post-seismic) displacements. Given the complex nature of rupture history in this region, the observed coseismic surface deformation may not fit fault parameters obtained from seismic sources. In such case, the estimate of a single moment tensor would be insuficcient. The USGS moment tensor is consistent with a 56% double-couple mechanism. This, combined with a resulting tsunami smaller than expected, might indicate a complex, multiple rupture system analogous to 2016 Amatrice-Norcia (Improta et al., 2019) and Kaikoura (Xu et al., 2018) events.

Presenting Author: Margarita M. Solares-Colón

Authors