2008 1 11 M4.7 On the M4.7 earthquake off Kamaishi, Iwate prefecture, Japan, on January 11, 2008. Graduate School of Science, Tohoku University 2008 1 11 M4.7 Matsuzawa et al. (2002) M-T M4.9 23Hz DD Waldhauser and Ellsworth, 2000 M4.9 M-T M4.9 1995 2001 Okada et al. (2003) Ito et al. (2005) CMT 1995 10% Mw 0.1 Imanishi and Ellsworth, Source scaling relationships of microearthquakes at Parkfield, CA, determined using the SAFOD Pilot Hole Seismic Array, Geophys. Monogr., 170, AGU, 2006. Ito et al., Spatial distribution of centroid moment tensor solutions for the 2004 off Kii peninsula earthquakes, EPS, 57, 351-356, 2005. Matsuzawa et al., Characteristic small-earthquake sequence off Sanriku, northeastern Honshu, Japan, GRL, 29, doi:10.1029/2001gl014632, 2002. Okada et al., Comparison of source areas of M4.8±0.1 repeating earthquakes o Kamaishi, NE Japan: are asperities persistent features?epsl, 213, 361-374, 2003. Uchida et al., Source parameters of a M4.8 and its accompanying repeating earthquakes off Kamaishi, NE Japan - implications for the hierarchical structure of asperities and earthquake cycle, GRL, 34, doi:10.1029/2007gl031263, 2007. Waldhauser and Ellsworth, A double-difference earthquake location algorithm: Method and application to the Northern Hayward fault, California, BSSA, 90, 1353-1368, 2000.
Fig.1 M4.9 Matsuzawa et al., 2002 (A) M6 19261998 (B) 19951999 (C) (B) M4.9 Location of the 'characteristic earthquakes' off Kamaishi (Matsuzawa et al., 2002). (A) Epicenter distribution of events with M6 or larger (1926-1998; JMA catalogue). (B) Epicenter distribution of microearthquakes (1995-1999; Tohoku University catalogue). (C) Close up of the rectangle shown in Fig.1(B). The cluster containing the characteristic events is surrounded by a rectangle and indicated by an arrow. Fig.2 M-T M4 1995 M5.1M4 1976 2003 5 2008 M5.02008 2008 1 11 8:00 1 9 10:41 M1.7 2 10 1 11 8:26 M1.0 8:32 M0.5 M-T diagram for the characteristic earthquake cluster, off Kamaishi. Displacement magnitudes determined by JMA are shown for events larger than M4. Only the events after 1975 are shown for events less than M4.
Fig.3 M4.9 160km 5 UD component seismograms observed at AOB (epicentral distance is about 160 km) for the recent five events. Fig.4 1995 DD 38MPa 2008 M4.7 1995 M5.0) 2001 M4.8 Hypocenter distribution of the earthquakes in and after 1995 determined using DD method. Radius of each circle is calculated assuming the stress drop is 38MPa. The scalar moment is estimated from JMA magnitude. Red large circle denotes the 2008 event.
Multi Window Spectral Ratio Imanishi and Ellsworth, 2006 38 1995 4 2008 M2.4 M-T Fig.5 Source sizes of events estimated using Multi Window Spectral Ratio Method (Imanishi and Ellsworth, 2006). Color indicates the stress drop. The centroids of the earthquakes are projected onto a plane parallel to the plate boundary (westward dipping at 38 degrees). Bottom figure indicates the M-T diagram. In the diagram, groups are indicated by symbols.
Fig.6 1995 2001 Okada et al., 2003 Best double couple solutions for the 1995 (left) and 2001 (right) events estimated by Okada et al. (2003). Fig.7 2008 1 11 CMT F-net CMT solution for the event on January 11, 2008. F-net station data are used in the analysis.
Fig.8 1995 2001 2008 0.25 Slip distributions for the 1995, 2001 and 2008 events estimated from broadband seismograph data using an empirical Green's function method. Small circles indicate the epicenters. Each distribution is normalized by its maximum slip. Fig.9 1995 2001 2008 KGJDITHMK STS-2 0.12.0Hz 2001 2008 1995 Comparison of the broadband seismographs between the 1995, 2001 and 2008 events at stations KGJ, DIT and HMK. Note that the seismographs for the 1995 events are little different from others.
1995 2001 2008 Table 1 Comparison of the seismic moments between the 1995, 2001 and 2008 events.