Detection of tremors in the Marlborough region and its relationship with the 2016 Mw 7.9 Kaikoura (New Zealand) earthquake

Abstract

<p>Seismic tremor has previously been reported in the Marlborough (New Zealand) region, with detections made using the national GeoNet network. However, because of the sparsity of that network, only 40 tremors were detected using 6 stations. We conducted a similar analysis again, but this time using data from 4 stations from the GeoNet network as well as 16 stations from a local campaign network, bringing the total number of stations to 20. Our new tremor catalog contains 4699 tremors (around 100 times more events than the previous catalog) and spans the period 2013-2019 which include the major 2016 Mw7.9 Kaikoura earthquake. Based on our current knowledge, that makes the Marlborough region the most active region for tremors in New Zealand.</p><p> </p><p>The observed tremor in the region are split into two clusters, separated by a gap of around 20 km. The South-West cluster has an elongated shape in the direction of the upper-plate dextral strike-slip (Hope and Clarence) faults. The occurrence of tremor before the Mw 7.9 Kaikoura earthquake is fairly constant over time. After the earthquake however we observe  a strong acceleration in the rate of tremor, that slowly recovers over time. At the end of the analysis (May 2019), more than 2 years after Kaikoura earthquake, the tremor burst rate has still not recovered to the previous rate before the earthquake. We also observe several episodes of tremor migration, with a migration velocity of around ~50km/day, most of the migration being from South-West to North-East.</p><p> </p><p>This new tremor catalog provides a unique opportunity to better understand possible interaction of a major earthquake with the tremor activity and will help to better understand the local tectonic activity of the Marlborough region.</p><p> </p>