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Investigating Slow Slip Transients and Earthquake Swarms on the Blanco Transform Fault With Obs Data Mining

Description: 

Oceanic transform faults (OTFs) constitute one type of plate boundary accommodating deformation through quasi-periodic earthquakes, aseismic creep and seismic swarms. Recent studies suggest that earthquake swarms are driven by episodic slow slip, both of which can sometimes precede moderate-large earthquakes at OTFs. Here, we analyze data from an OBS network (X9 code, 55 stations deployed for 1 year in 2012-2013, Nabelek et al 2012) surrounding the Blanco Transform Fault (BTF) located offshore Oregon. We re-visit this dataset using two advanced data mining approaches. We thus conduct a comprehensive analysis of the BTF seismic wavefield, aiming to investigate slow slip phenomena and its role in generating earthquake swarms.

First, we apply a machine-learning (ML) workflow to detect micro-seismicity. We use the PickBlue CNN phase picker and GaMMA associator. After a quality assessment, about 40,000 earthquakes are retained, representing 4.5 times more than a previous seismic catalog for the same dataset. Our ML seismic catalog delineates the fault's along-strike segmentation, revealing distinct seismogenic behaviors: sections emitting nearly continuous microseismicity, aseismic areas, and portions characterized by seismic swarms, and mainshock - aftershock sequences. Second, we measure the seismic wavefield spatial coherence across the OBS network, by computing the covariance matrix spectral width, using CovSeisNet. An interesting finding includes very low-frequency earthquakes (VLFE) detection in the 10-30 s period range.

To better understand the spatio-temporal relations between slow earthquakes, foreshock swarms, and mainshock earthquakes, we are relocating seismic swarms and VLFE sources. Finally, we aim to extend the new insights gleaned using the year with OBS data on the fault, to improve and ground truth methods using only the permanent in-land stations near the coast. This would improve quality and reliability of multi-year analysis of BTF swarms when only in-land stations exist, aiding in the elucidation of their driving mechanisms, potentially involving slow slip transients.

Session: Advances in Operational and Research Analysis of Earthquake Swarms - I

Type: Oral

Date: 5/3/2024

Presentation Time: 02:15 PM (local time)

Presenting Author: Cyril

Student Presenter: No

Invited Presentation: 

Authors