Step-like migration of early aftershocks following the 2007 M_w 6.7 Noto-Hanto earthquake, Japan

Abstract

Seismic data reveal that the aftershock zone expands with time after a main shock event. Here we examine the aftershock sequence recorded during the first 32 days following the 2007 Noto-Hanto earthquake, Japan. By applying a matched-filter technique to the data, we detected about 10 times more events than those listed in the routinely constructed earthquake catalog. The aftershock area expanded along the fault strike as a logarithmic function of time, beginning immediately after the main shock. Aftershock expansion toward the SW was especially extensive and developed more rapidly than toward the NE. Interestingly, the aftershock area expanded in a step-like manner by the activation of a series of spatially clustered seismic bursts. Spatial correlation between the aftershock extension and the afterslip distribution suggests that the expansion of the aftershock area could be mainly driven by aseismic afterslip. The aftershock area continues to expand, even though 7 years have now passed since the main shock.

Spatial‐temporal evolutions of early aftershocks following the 2013 Mw 6.6 Lushan earthquake in Sichuan, China

“…Our observations of aftershock expansions since the Lushan main shock are generally consistent with other recent studies of early aftershocks following moderate‐to‐large shallow earthquakes [e.g., Chang et al , ; Peng and Zhao , ; Lengline et al , ; Tang et al , ; Kato and Obara , ; Meng and Peng , ; Yao et al , ]. Except Chang et al [] (in which they handpicked the first hour of aftershocks following the 1999 M w 7.6 Chi‐Chi earthquake), other studies utilized a similar MFT technique to detect potential missing aftershocks in the first few hours or days following the main shocks.…”

“…Improvements on aftershock detections have been done by hand picking from high‐frequency filtered waveforms [ Enescu et al , ; Peng et al , , ], which is subjective and time‐consuming. Recent several studies utilized a so‐called Matched Filter Technique (MFT) to automatically detect aftershocks following recent moderate‐to‐large earthquakes [e.g., Peng and Zhao , ; Lengline et al , ; Kato and Obara , ; Tang et al , ; Holtkamp and Ruppert , ; Meng and Peng , ]. These studies generally used existing aftershocks in known catalogs as templates and scanned through continuous waveforms to search for events with high waveform similarities.…”

Detailed spatiotemporal evolution of microseismicity and repeating earthquakes following the 2012 Mw 7.6 Nicoya earthquake

“…To better define the aftershock expansion pattern, we followed recent work by Kato and Obara [] and defined the activation of aftershocks at the time when the cumulative numbers of aftershocks within a 5 km wide zone (either along or perpendicular to the trench) exceed a certain number N . We slid the window per 1 km in order to achieve a better spatial resolution.…”

“…Similar to other moderate to large main shocks with migrating aftershocks [ Peng and Zhao , ; Kato and Obara , ; Tang et al ., ], we also observed a complex expansion of aftershocks with time (Figure ). The complexity in activation of aftershocks could be due to the fact that we simply assign the template location to the best detected event, and a better way to examine the spatiotemporal evolution may be to perform relocations for all the newly detected events.…”

Why Do Aftershocks Occur Within the Rupture Area of a Large Earthquake?

“…A simple explanation of this mainshock-aftershock sequence is that the mainshock reduces strain energy in the rupture area and redistributes part of the energy to surrounding faults, which is then released during the aftershocks (Stein, 1999). Temporal expansion of the aftershock area is commonly observed and is explained by the spatial expansion of afterslip (Henry & Das, 2001;Kato & Obara, 2014;Perfettini et al, 2018;Uchida et al, 2004). Temporal expansion of the aftershock area is commonly observed and is explained by the spatial expansion of afterslip (Henry & Das, 2001;Kato & Obara, 2014;Perfettini et al, 2018;Uchida et al, 2004).…”