Geodetic imaging of plate motions, slip rates, and partitioning of deformation in Japan

Abstract

[1] Interseismic deformation in Japan results from the combined effects of tectonic processes including rotation of crustal blocks and the earthquake cycle process of elastic strain accumulation about upper plate faults and subduction zone interfaces. We use spherical linear block theory constrained by geodetic observations from densely spaced Global Positioning System (GPS) stations to estimate plate motions, fault slip rates, and spatially variable interplate coupling on the Japan-Kuril, Sagami, and Nankai subduction zones. The reference model developed in this paper consists of 20 blocks, produces a mean residual velocity magnitude of 1.84 mm/yr at 950 stations, and accounts for 96% of the observed interseismic deformation signal. We estimate fault slip rates in excess of 15 mm/yr along the Niigata-Kobe Tectonic Zone and Itoigawa-Shizuoka Tectonic Line through central Japan, confirming their hypothesized roles as major tectonic boundaries. Oblique convergence across the Nankai Trough is partitioned, with 3/4 of the $30 mm/yr of trench-parallel motion accommodated by strike-slip motion on the subduction interface and the remaining 1/4 accommodated by right-lateral slip on the Median Tectonic Line. In contrast, our models suggest negligible slip partitioning in eastern Hokkaido, where oblique slip on the Japan-Kuril subduction interface accommodates all of the trench-parallel component of relative plate motion. Inferred spatial variations in the rake and magnitude of slip deficit on subduction zone interfaces reflect the influences of megathrust geometry and earthquake cycle processes such as enhanced elastic strain accumulation about seismic asperities and coseismic sense fault motion indicative of silent slip events or afterslip following large earthquakes.

Static slip model of the M w 9.0 Tohoku (Japan) earthquake: Results from joint inversion of terrestrial GPS data and seafloor GPS/acoustic data

“…In addition, the length of the rupture area with a slip >10 m is about 240 km, extending from 39.6 to 36.97°N and mostly located at depths shallower than 40 km. The derived slip concentration is generally consistent with the highly "coupled" area inferred from inter-seismic terrestrial observations [17,18]. However, it seems that the highly coupled area is just deeper than the area of concentrated slip and closer to the coastline of northeastern Japan.…”

A very long-term transient event preceding the 2011 Tohoku earthquake

“…In addition, stationary westward trends were obtained at all stations for the seismic quiescence period before 2002 (red lines in Fig. 1b), and we assumed that these represent regular deformations that were due to slip deficit, as in all previous studies [13][14][15][16] . We conducted an additional analysis of the time series; the results shown in Supplementary Note 1 and Supplementary Fig.…”

“…We use a data set from the dense Global Positioning System (GPS) network GEONET, operated by the Geospatial Information Authority of Japan (GSI). In previous studies [13][14][15][16] , the slip deficit rate in the JTSZ was imaged using partial data sets covering the period of seismic quiescence before the 2003 Tokachi-oki earthquake. In this study, we use the whole data set from 21 March 1996 to 8 March 2011 (one day before the foreshock).…”

Accelerated pacific plate subduction following interplate thrust earthquakes at the Japan trench

“…inter-plate coupling is relatively high (Hashimoto et al, 2009;Loveless and Meade, 2010) except the boundary between Segments 3 and 4 (Ye et al, 2012), and it is difficult to attain the landward velocity anomaly by simply increasing the inter-plate friction. We hence hypothesize that the decoupling at Segments 2 and 4 temporarily accelerated the subduction of the Pacific Plate over a multi-segment scale in NE Japan and enhanced coupling in Segments 1 and 3.…”