Local Earthquake Tomography in the Northern Hikurangi Margin (New Zealand) Using a Detailed Offshore and Onshore Microseismicity Catalog

Date: 4/25/2019

Time: 06:00 PM

Room: Grand Ballroom

The northern Hikurangi margin in New Zealand has produced remarkable tectonic events, including tsunami earthquakes and dozens of slow slip events in the last ten to fifteen years. Records of microseismicity over time throughout the Hikurangi trough help uncover the physical features of the subduction zone. Exploiting seismic data from temporal ocean bottom seismometers deployed during a 2014-2015 experiment and permanent land stations maintained by GeoNet, we built a comprehensive offshore and onshore microseismicity catalog with 2,313 earthquakes. The seismicity is mainly located along the plate interface and within the downgoing slab, with an interesting 20 km-wide microseismicity gap near the coast. However, this catalog was built using 1D P- and S-wave velocity models that do not fully account for the complexity of this subduction zone. To improve the hypocenter locations with a regionally-constrained velocity model and further explore the relationships of microseismicity with slow slip events, we constructed a 3D local earthquake tomography model. We use the tomography code SIMUL2000 to iteratively perform a full matrix inversion of absolute P and S-P arrival times, obtain relocated hypocenters, and generate 3D velocity models for Vp and Vp/Vs. These results can be compared to seismically image and better understand the Hikurangi subduction zone. Furthermore, increasing fluid pressure from subducted sediments has been suggested to trigger the occurrence of slow slip events in active subduction zones. The 3D velocity models enable us to test this hypothesis and probe the distribution of high and low fluid pressure regions in this subduction zone. Thus, investigating the spatial variations of velocities along the northern Hikurangi margin offer new insights into recognizing the physical mechanisms controlling the occurrence of slow slip events and microearthquakes.

Presenting Author: Jefferson Yarce

Authors