Relation between similar aftershocks and ruptured asperity of a large inland earthquake: Example of the 2007 Noto Hanto earthquake

Abstract

We investigate spatial distribution of similar aftershocks of a large inland earthquake using waveform data obtained by a dense temporary seismic network. Similar earthquakes on the source fault are mainly located around the deeper edge of the major asperity. The cumulative slip estimated from the similar earthquakes ranges from 0.6 to 2.7 cm and coincides with the slip estimated from postseismic crustal movement observed by GPS. The slip velocity estimated from both the slip and the recurrence interval of the similar earthquakes is larger at the edge of the asperity. These results suggest that the afterslip area is spatially complementary to the asperity on the fault surface for inland earthquakes similar to large interplate earthquakes on the plate interface.

Spatial distribution of similar aftershocks of a large inland earthquake, the 2000 Western Tottori earthquake, in Japan

“…They showed that similar aftershocks on the source fault are located mainly around the deeper edge of the major asperity. This result suggests that the afterslip area is spatially complementary to the asperity on the fault surface for inland earthquakes similar to large interplate earthquakes on the plate interface (Hiramatsu et al, 2011). However, to confirm this possibility, we must examine the existence and the spatial distribution of similar aftershocks for other large inland earthquakes.…”

“…Our procedure to detect similar aftershocks follows that applied by Hiramatsu et al (2011). First, we select pairs of aftershocks of which the cross-correlation coefficients in a 10-s time window of 1-4 Hz band-pass filtered waveforms are greater than 0.95 at more than five stations.…”

“…In this case, we judge that these events are not similar aftershocks. A detailed methodology to judge similar aftershocks for more complicated cases is described in Hiramatsu et al (2011).…”

“…The slip of each event is estimated from extrapolation of the empirical relation, d = 1.56×10 −7 ×M o 1/3 , between the scalar moment M o (dyne·cm) and the slip d (cm) reported by Somerville et al (1999). Hiramatsu et al (2011) pointed out that this relation provided reasonable values for similar aftershocks of the 2007 Noto Hanto earthquake-an inland earthquake-in contrast to the relation reported by Nadeau and Johnson (1998) for repeating earthquakes at a plate boundary, that has been applied to the case of repeating earthquakes in California (Nadeau and McEvilly, 1999), in northeastern Japan (Igarashi et al, 2003;Uchida et al, 2004Uchida et al, , 2009Matsuzawa, 2011), in Sumatra (Yu et al, 2013), and in Taiwan (Chen et al, 2008).…”

“…A distribution of repeating earthquakes before the 2011 off the Pacific coast of Tohoku earthquake revealed a large afterslip area (Uchida and Matsuzawa, 2011). Recently, Hiramatsu et al (2011) examined similar aftershocks, which show high cross-correlation coefficients (≥ 0.95) of waveforms at the same station and share an almost identical source area, i.e., almost the same source location and the same focal mechanism, of the 2007 Noto Hanto earthquake. They showed that similar aftershocks on the source fault are located mainly around the deeper edge of the major asperity.…”