Abstract
Tectonic tremors have been detected in New Zealand, including the Gisborne and Manawatu regions in the North Island and along the Alpine Fault in the South Island. Here we report a regional analysis of tremor activity in New Zealand and present a potential relationship between slow and ordinary earthquakes. We first construct a tremor catalog in the Cape Turnagain, Marlborough, and Puysegur regions that spans the 2005–2016 time period using the GeoNet permanent seismometer network, and extend the tremor catalog in Manawatu to cover the same period. We employ an envelope cross-correlation method to detect and locate the seismic events, then extract the tremor-like events using a scaling-law-based criterion that is a function of the event duration and seismic energy, and finally select the tremors by visual inspection. We find that the tremors in Cape Turnagain temporally coincide with known shallow slow slip events in the region. We are also able to relate the increased tremor rates during 2010–2011 and 2014–2015 to two deep slow slip events in Manawatu. However, known slow slip events cannot explain all the increases in the tremor rate throughout Manawatu. Tremors in the South Island occur near recent large earthquakes, such as the 2016 Mw 7.8 Kaikoura Earthquake in Marlborough and 2009 Mw 7.6 Dusky Sound Earthquake in Puysegur, suggesting a possible relationship between slow and fast tectonic processes.
Highlights
Tectonic tremors were first detected in Southwest Japan (Obara 2002) and have since been discovered in many regions that possess various tectonic settings, such as the subduction zones in Cascadia (Rogers and Dragert 2003), Mexico (Payero et al 2008), and south Chile (Ide 2012), a collision zone in Taiwan (Peng and Chao 2008), and the strike-slip fault system along the San Andreas Fault (Nadeau and Dolenc 2005)
This study focuses on tectonic tremors in New Zealand, which is at the interface between the Pacific and Australian Plates (Fig. 1)
We use a cross-correlation method, followed by the implementation of a scaling-law-based criterion and handpicking, to construct our tremor catalog. This allows us to build a tremor catalog, focusing on four different regions, despite the active seismicity observed in New Zealand
Summary
Tectonic tremors were first detected in Southwest Japan (Obara 2002) and have since been discovered in many regions that possess various tectonic settings, such as the subduction zones in Cascadia (Rogers and Dragert 2003), Mexico (Payero et al 2008), and south Chile (Ide 2012), a collision zone in Taiwan (Peng and Chao 2008), and the strike-slip fault system along the San Andreas Fault (Nadeau and Dolenc 2005). Tremor studies in New Zealand have generally proven difficult due to the high activity of ordinary earthquakes, which makes automatic detection and location challenging. We compare log(Es) and log (T ) for all the detected events in the Nankai region, Japan (Fig. 2a; Idehara et al 2014), and the four study regions in New Zealand (Fig. 2b) using the cross-correlation method.
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