The Intricate Relationship of the M7.8 Kaikoura Earthquake and Tremors

Session: From Aseismic Deformation to Seismic Transient Detection, Location and Characterization
Type: Oral
Date: 4/29/2020
Time: 05:15 PM
Room: 230 + 235
Description: 

Many tremors have been already detected throughout New Zealand, in North Island in Gisbourne, Manawatu and Cape Turnagain and in South Island, on Alpine fault and in Puysegur.

In this study we will focus more particularly on Marlborough, in a region that was subject to the Mw 7.8 2016 Kaikoura earthquake. The role of the subduction zone in this earthquake is debated, as it is not sure that it played a role in the earthquake, although after-slip seem to have occurred on it. Interestingly, we observed a migration of tremors 2 years before Kaikoura earthquake, from Northeast to Southwest, approaching the hypocenter of Kaikoura earthquake. Despite being speculative, this may indicate that a slow slip event is happening shortly before Kaikoura earthquake, which is supported by a small signal in two GPS stations nearby. After Kaikoura earthquake, we also observed an increase in tremor rate forming two clusters. The study of tremors in this region may provide information on the faults that played a role in Kaikoura earthquake (among them the role of the subduction) and the possible interaction of slow earthquakes with a crustal earthquake.

To detect and locate tremors, we use broadband and shortband velocity traces from the GeoNet network. The traces are bandpass filtered between 2-8Hz and transform into envelope. Then we apply a classic cross-correlation technic to detect and locate the events. To remove unexpected events (i.e.: earthquakes), we used a criteria base on seismic energy and duration. Finally, we manually check each velocity traces and spectrograms.

Presenting Author: Pierre Romanet

Authors