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From Foreshock Outset to Aftershock Decay: High-resolution Analysis of a Recent Earthquake Sequence in the Ecuadorian Subduction Margin

Description: 

It is quite rare for an earthquake sequence to be recorded at high resolution from its early preparatory phase throughout mainshock and aftershock decay. This is even more unusual for less explored subduction zones such as the Ecuadorian margin. Producing such detailed studies could lead to a better understanding of the physical mechanism behind rupture initiation and earthquake triggering in active margins.

On 27 March 2022, a Mw 5.8 earthquake occurred on the northern coast of Ecuador, near the town of Esmeraldas. Here we take advantage of a dense temporary seismic network in place at the time as part of an active seismic experiment (HIPER marine campaign, PIs A. Galve, A. Rietbrock), in order to detect and locate the whole of the local seismic sequence at high resolution. The continuous recordings of 100 short period seismometers are processed with a state of the art earthquake detection/location pipeline based on recently developed artificial intelligence methods. We also accurately relocate the whole sequence using a recently published local velocity model and relative relocation based on cross-correlation phase arrivals.

The results show more than 900 events within the first three days following the mainshock. The sequence starts with three small-magnitude (M<2) foreshocks 40 to 2 minutes before the mainshock, all of them within 1 km from the mainshock epicenter. The ensuing seismicity spreads over 10 km along the subduction interface, nicely delineating the SE-dipping megathrust. Early aftershocks (first 12 hours) nucleate near the mainshock hypocenter and down-dip of it, while later aftershocks nucleate mostly up-dip of the mainshock. Aftershock productivity quickly decreases during the first 16 hours following the mainshock, after which the seismicity rate sharply increases again due to the occurrence of the largest aftershock (Mw 5.2). Our study provides a unique opportunity to study in detail the spatio-temporal relationship among seismic events throughout all different stages of an earthquake sequence at an unprecedented scale for this region of the world.

Session: Deciphering Earthquake Clustering for the Better Understanding of Crustal Deformation Mechanisms

Type: Oral

Date: 4/20/2023

Presentation Time: 04:30 PM (local time)

Presenting Author: Andreas Rietbrock

Student Presenter: No

Invited Presentation: 

Authors