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Rupture Behavior of Large Strike-Slip Earthquakes at Equatorial Atlantic Oceanic Transform Faults: Constraints From Hydroacoustic Data

Oceanic transform faults (OTFs) are tectonic strike-slip plate boundaries that offset mid-ocean ridges by tens to hundreds of kilometers, thus reaching the globally largest oceanic offset with up to 900 km in the equatorial Atlantic Ocean (EAO). Earthquakes along OTFs can produce moment magnitudes (Mw) of >7, with global networks monitoring in real time. Previous studies used teleseismic data, numerical modeling, and thermal constraints to yield characteristics of the seismic rupture behaviors along the OTFs. In this study, we take a different approach by using hydroacoustic T-waves arriving at the International Monitoring System hydrophone triplet deployed at Ascension Island and belonging to the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO) to study the rupture of 43 strike-slip earthquakes in the EAO. The earthquakes occurred along nine OTFs in EAO with 5.6>Mw<7.1 reported by the Global Centroid Moment Tensor catalog. We use cross-correlation and arrival-time difference variations to identify the T-wave source directions (back-azimuth) and compare interceptions of the directions with mapped fault traces from multibeam bathymetric data to reveal the total rupture length of the earthquakes. Our technique is based on sound propagation through the ocean and provides a new alternative characterization of the rupture behavior of large strike-slip earthquakes. Our preliminary results show rupture lengths reaching from 5.34±1.0 to 101.98±12.8 km and rupture velocities between 0.83±0.29 and 4.5±0.8 km/s, with a well-correlated least-square regression between the rupture length and Mw. Most of the earthquakes show a unilateral rupture moving. Furthermore, we also identified a two-stage (eastward and westward) rupture propagation to the 2016 Mw 7.1 Romanche earthquake like results published by a recent study. This complex two-stage rupture style was similarly observed in the 2022 Mw 6.6 Vema earthquake. Therefore, we show that rupture parameters of large strike-slip earthquakes in OTFs can be revealed not just by commonly used teleseismic methods but also by solely using hydroacoustic data.

Session: Marine Seismoacoustics - I

Type: Oral

Room: Tikahtnu Ballroom E/F

Date: 5/1/2024

Presentation Time: 04:30 PM (local time)

Presenting Author: Guilherme de Melo

Student Presenter: Yes

Additional Authors