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Analysis of Repeating Earthquakes Near the Locking Transition of New Zealand's Hikurangi Subduction Zone

Session: Waveform Cross-Correlation-Based Methods in Observational Seismology [Poster]

Type: Poster

Date: 4/21/2021

Presentation Time: 03:45 PM Pacific

Description: 

The Hikurangi subduction zone beneath eastern North Island, New Zealand, exhibits a variety of fault-slip related phenomena. The northern Hikurangi margin hosts shallow slow-slip and is weakly coupled to shallow depths on inter-seismic timescales. In contrast, the southern Hikurangi margin is strongly coupled beneath the southern North Island, and only deep slow-slip has been observed. The transition in coupling occurs beneath the township of Porangahau, and is an exemplary focus region for studying how this along-strike change in locking is accommodated.

To examine slip processes at this key transition zone, we have constructed and analysed a catalogue of repeating earthquakes that occurred over a period of 14 years between 2004 and 2018. To build our catalogue we first clustered GeoNet's extensive earthquake catalogue by distance and correlation using weak constraints to identify potentially repeating events. We then used a stronger cross-correlation threshold of at least 0.95 normalised cross-correlation on three or more stations to identify repeating earthquakes from the initial clusters. This threshold was determined by our group's previous work on the northern Hikurangi margin.

We computed precise absolute locations and focal mechanisms of all 225 families and their constituent earthquakes via a combination of manual phase-picking and cross-correlation pick-correction. This analysis yields 225 families of 532 repeating earthquakes, with some of them containing as many as nine events in the span of >10 years. Because repeating earthquakes represent cyclic loading, they can be used to detect temporal and spatial changes of slip-rate at depth and hence monitor how stress is transferred to seismogenic zones. This analysis of repeating earthquakes and their changes in time improves our understanding of how the Hikurangi subduction zone is being loaded at this transition zone.

Presenting Author: Olivia D. Pita-Sllim

Student Presenter: Yes

Authors