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Insar Measurement of the Coseismic and Postseismic Displacements From the 2020 Southwest Puerto Rico Seismic Sequence

Description: 

We analyzed synthetic aperture radar (SAR) images from the Advanced Land Observation Satellite-2 (ALOS-2) satellite operated by Japan Aerospace Exploration Agency and the Copernicus Sentinel-1A and -1B satellites operated by the European Space Agency for the earthquakes near the southwest coast of Puerto Rico from January through July 2020. We use SAR interferometry (InSAR) measurements of displacements in the radar line-of-sight directions and time-series analysis of the InSAR to improve extraction of coseismic signals. We combine data from different radar look directions to estimate two components of the surface displacement, and we concentrate on the east and vertical components. The large-scale deformation due to slip at depth is dominated by vertical downward motion in and around the Guayanilla Bay with an amplitude of about 20 cm, accompanied by westward motion on the east side and eastward motion on the west side, all consistent with normal fault slip on a generally north-dipping fault plane. InSAR on land does not constrain the strike of the main fault, but the north-west dipping nodal plane of the USGS moment tensor for the main magnitude 6.4 is consistent with the InSAR and is also consistent with relocated hypocenters (HypoDD) of early aftershocks. In addition to the larger displacements likely caused by the magnitude 6.4 mainshock, the ALOS-2 InSAR pair, which spans the time from September 2019 to 20 January 2020, shows that there was fault slip of part of the Punta Montalva Fault between Punta Montalva and Punta Brea. If we assume purely horizontal deformation, the InSAR line-of-sight signal is consistent with 8 cm of left-lateral slip at the surface, during one of the large foreshocks or aftershocks. The longer radar wavelength of ALOS-2 (24 cm) enables InSAR measurements in the more vegetated Punta Montalva-Punta Brea area that is low coherence with Sentinel-1 radar (6 cm wavelength). Additional analysis of Sentinel-1 images acquired between January and June show that the Punta Montalva Fault likely had additional slip at the surface after mid-January that may be related to large aftershocks.

Session: The 2020-2021 Southwest Puerto Rico Seismic Sequence: Current State of Knowledge and Implications

Type: Oral

Date: 4/18/2023

Presentation Time: 08:45 AM (local time)

Presenting Author: Eric J. Fielding

Student Presenter: No

Invited Presentation: 

Authors