Plate boundary slip associated with the 2003 Off-Tokachi earthquake based on small repeating earthquake data (original) (raw)
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Geophysical Research Letters
A decadal-scale deformation transient preceding the 2011 M w 9 Tohoku-oki, Japan, earthquake was reported from continuous GPS data and interpreted as accelerating aseismic slip on the Japan Trench megathrust. Given the unprecedented nature of this transient, independent confirmation of accelerating slip is required. Here we show that changes in the recurrence intervals of repeating earthquakes on the Japan Trench megathrust in the period 1996 to 2011 are consistent with accelerating slip preceding the Tohoku-oki earthquake. All sequences of repeating earthquakes with statistically significant trends in recurrence interval (at 95% confidence) offshore south central Tohoku occurred at an accelerating rate. Furthermore, estimates of the magnitude of slip acceleration from repeating earthquakes are consistent with the completely independent geodetic estimates. From a joint inversion of the GPS and seismicity data, we infer that a substantial portion of the megathrust experienced accelerating slip, partly surrounding the eventual rupture zone of the M w 9 earthquake.
We analyzed continuous GPS data to investigate the spatial distribution of post-seismic slip associated with two large earthquakes of October 19 and December 2, 1996, in Hyuga-nada, Japan. We found that the moment release due to post-seismic events was comparable to the co-seismic moment release during the two earthquakes. The source parameters of the first post-seismic event are as follows: the moment release = 1.7 × 10 19 Nm; the maximum slip = 0.06 m at about 50 km northwest from the epicenter of the first earthquake; the characteristic decay time (= final slip/initial slope) = 15 days. For the second post-seismic event, the moment release = 2.0 × 10 19 Nm; the maximum slip = 0.13 m at about 15 km northwest from the epicenter of the second earthquake; the characteristic time = 100 days. In both events, the slip vectors of the downgoing Philippine Sea (PHS) Plate on the SW-striking interplate boundary are directed west, in accordance with the co-seismic slip. It is also shown that the sites for co-seismic slip, post-seismic slip, and aftershocks do not overlap but complementarily share the plate boundary. This suggests that individual sites are characterized by their own constitutive laws, which may control modes of moment release as well as the entire sequence.
Coseismic and postseismic slip of the 2011 magnitude-9 Tohoku-Oki earthquake
Nature, 2011
This paper reports the overview of the crustal deformation caused by the 2011 off the Pacific coast of Tohoku Earthquake (hereafter referred as "the Tohoku Earthquake"), detected by GEONET, the GPS continuous observation system operated by GSI. We found very wide area of Japanese Islands was remarkably affected by the crustal deformation caused by the main shock of the Tohoku Earthquake, from Hokakido to Kinki district. We estimated the geometry of the seismogenic fault of the Tohoku Earthquake, as well as the slip model on the plate boundary between the Pacific plate and the North American plate, from the crustal deformation data. The length of the fault is estimated longer than 400 km from off Iwate prefecture in the north to off Ibaraki prefecture in the south. The largest slip estimate on the plate boundary is more than 56 m at the off Miyagi region near the Japan trench. The postseismic crustal deformation is also observed by GEONET. This means slow postseismic slip is ongoing along the plate boundary around the main fault zone.
Slow Slip Following the 2003 Tokachi-oki M8 Earthquake off Hokkaido
2010
A Sacks-Evertson borehole strainmeter has operated since 1982 at Urakawa Seismological Observatory (KMU) of Hokkaido University in the southern part of the Hidaka Mountains. The site is 105 km NW of the epicenter of the 2003 Tokachi-oki earthquake (M8.0). We use State Space Modeling (Kitagawa et al., 2010) to remove strains due to earth tides, air pressure variations and precipitation. After the earthquake the data showed a clear episode of contraction for 4 days followed by expansion for 23 days. These signals correlate with increased aftershock seismicity for M>4 events. These strain changes, together with surface displacements detected by a temporary GPS network, are indicative of propagation of slow slip at depth (e.g. Geographical Survey Institute,2004). We use quasistatic calculations to generate synthetic waveforms for the measured quantities. Initial choices for source parameters are guided by the parameters of the main shock on the basis that the slow slip takes place on...
2012
We investigated the crustal deformation associated with the 2011 off the Pacific coast of Tohoku Earthquake (M 9.0) that occurred on March 11, 2011, along the plate boundary off Tohoku district, northeastern Japan, based on dense GPS observation. Coseismic displacements due to this event were applied to estimate the causal interplate slip by means of a geodetic inversion analysis. The major slip area is located around the asperities of the 1981 Miyagi-oki (M 7.2) and 2003 Fukushima-oki (M 6.8) earthquakes and the maximum slip is estimated as being up to 35 m. The estimated slip distribution suggests that the asperities of the Miyagi-oki earthquake in 1978 (M 7.4) that had not been ruptured during the Miyagi-oki earthquake in 2005 were ruptured as a part of the main shock fault of the 2011 off the Pacific coast of Tohoku Earthquake.
Nature Communications, 2016
Large interplate earthquakes are often followed by postseismic slip that is considered to occur in areas surrounding the coseismic ruptures. Such spatial separation is expected from the difference in frictional and material properties in and around the faults. However, even though the 2011 Tohoku Earthquake ruptured a vast area on the plate interface, the estimation of high-resolution slip is usually difficult because of the lack of seafloor geodetic data. Here using the seafloor and terrestrial geodetic data, we investigated the postseismic slip to examine whether it was spatially separated with the coseismic slip by applying a comprehensive finite-element method model to subtract the viscoelastic components from the observed postseismic displacements. The high-resolution co-and postseismic slip distributions clarified the spatial separation, which also agreed with the activities of interplate and repeating earthquakes. These findings suggest that the conventional frictional property model is valid for the source region of gigantic earthquakes.
Geophysical Research Letters, 1999
We report a "slow thrust slip event" that occurred beneath the Bungo Channel region, southwestern Japan. On Oct. and Dec., 1996, two Hyuganada earthquakes (both M w = 6.7), followed by afterslips, occurred. In addition, a crustal movement characterized by an extremely slow rise was observed around the Bungo Channel, about 200 km north from the epicenters, and continued for about 300 days long. Assuming a slow slip on the plate boundary, we estimate its duration and surface displacements from GPS time series data by curve-fitting, and then, determine the fault slip distribution. We found that a slow slip without any earthquakes continued for nearly one year and released the seismic moment comparable to that of the Hyuganada earthquakes. Occurrence of the slow thrust slip event suggests that this kind of event may be a characteristic mode of stress release at a transition region of interplate coupling.