[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.

[1] Imaging the extent to which the rupture areas of great earthquakes coincide with regions of pre-seismic interplate coupling is central to understanding patterns of strain accumulation and release through the earthquake cycle. Both geodetic and seismic estimates of the coseismic rupture extent for the March 11, 2011 M W = 8.9-9.0 earthquake Tohoku-oki earthquake may be spatially correlated (0.26 ± 0.05 to 0.82 ± 0.05) with a region estimated to be partially to fully coupled in the interseismic period preceding the earthquake, though there is substantial variation in the estimated distribution and magnitude of coseismic slip. The ∼400 km-long region estimated to have slipped ≥4 m corresponds to an area of the subduction zone interface that was coupled at ≥30% of long-term plate convergence rate, with peak slip near a region coupled ≥80%. The northern termination of rupture is collocated with a region of relatively low (<20%) interseismic coupling near the epicenter of the 1994 M W = 7.6 Sanriku-oki earthquake, and near a region of potential longterm low coupling or ongoing slow slip. Slip on the subduction interface beneath the coastline (40-50 km depth) is best constrained by the land-based GPS data and least constrained on the shallowest portion of the plate interface due to the ∼230 km distance between geodetic observations and the Japan trench. Citation: Loveless, J. P., and B. J. Meade (2011), Spatial correlation of interseismic coupling and coseismic rupture extent of the 2011 M W = 9.0 Tohoku-oki earthquake,

The spatial complexity of continental deformation in the greater Tibetan Plateau region can be defined as the extent to which relative motion of the Indian and Asian plates is partitioned between localized slip on major faults and distributed deformation processes. Potency rates provide a quantitative metric for determining the magnitudes of on-fault and diffuse crustal deformation, which are proportional to fault slip rates and strain rates within crustal micro-plates, respectively. We simultaneously estimate micro-plate rotation rates, interseismic elastic strain accumulation, fault slip rates on major structures, and strain rates within 24 tectonic micro-plates inferred from active fault maps in the greater Tibetan Plateau region using quasi-static block models constrained by interseismic surface velocities at 608 GPS sites and 9 Late Quaternary geologic fault slip rates. The joint geodetic-geologic inversion indicates that geologic slip rates are kinematically consistent with and result from differential micro-plate motions. Estimated left-lateral slip rates on the Altyn Tagh, west-central Kunlun, and Xianshuihe faults are relatively homogeneous along strike (∼11.5, 10.5, and 12 mm/yr, respectively)

[1] Deformation measured by regional GPS networks in continental plateaus reflects the geologic and tectonic variability of the plateaus. For two collisional plateaus (Tibet and Anatolia) and one noncollisional (the Altiplano), we analyze the regional strain and rotation rate by inverting GPS velocities to calculate the full two-dimensional velocity gradient tensor. To test the method, we use gridded velocities determined from an elastic block model for the eastern Mediterranean/ Middle East region and show that to a first order, the deformation calculated directly from the GPS vectors provides an accurate description of regional deformation patterns. Principal shortening and extension rate axes, vertical axis rotation, and two-dimensional (2-D) volume strain (dilatation) are very consistent with long-term geological features over large areas, indicating that the GPS velocity fields reflect processes responsible for the recent geologic evolution of the plateaus. Differences between geological and GPS descriptions of deformation can be attributed either to GPS networks that are too sparse to capture local interseismic deformation, or to permanent deformation that accrues during strong earthquakes. The Altiplano has higher internal shortening magnitudes than the other two plateaus and negative 2-D dilatation everywhere. Vertical axis rotation changes sign across the topographic symmetry axis and is due to distributed deformation throughout the plateau. In contrast, the collisional plateaus have large regions of quasi-rigid body rotation bounded by strike-slip faults with the opposite rotation sense from the rotating blocks. Tibet and Anatolia are the mirror images of each other; both have regions of positive dilatation on the outboard sides of the rotating blocks. Positive dilatation in the Aegean correlates with a region of crustal thinning, whereas that in eastern Tibet and Yunnan province in China is associated with an area of vertical uplift. Rollback of the Hellenic trench clearly facilitates the rotation of Anatolia; rollback of the Sumatra-Burma trench probably also enables rotation about the eastern syntaxis of Tibet. Citation: Allmendinger, R. W., R. Reilinger, and J. Loveless (2007), Strain and rotation rate from GPS in Tibet, Anatolia, and the Altiplano, Tectonics, 26, TC3013,

During the interseismic phase of the earthquake cycle, between large earthquakes, stress on faults evolves in response to elastic strain accumulation driven by tectonic plate motions. Because earthquake cycle processes induce non-local stress changes, the interseismic stress accumulation rate on one fault is infl uenced by the behavior of all nearby faults. Using a geodetically constrained block model, we show that the total interseismic elastic strain fi eld generated by fault interactions within Southern California may increase stressing rates on the Mojave and San Bernardino sections of the San Andreas fault within the Big Bend region by as much as 38% relative to estimates from isolated San Andreas models. Assuming steady fault system behavior since the C.E. 1857 Fort Tejon earthquake, shear stress accumulated on these sections due only to interaction with faults other than the San Andreas reaches 1 MPa, ~3 times larger than the coseismic and postseismic stress changes induced by recent Southern California earthquakes. Stress increases along Big Bend sections coincide with the greatest earthquake frequency inferred from a 1500-yr-long paleoseismic record and may affect earthquake recurrence intervals within geometrically complex fault systems, including the sections of the San Andreas fault closest to metropolitan Los Angeles.

Geodetic observations of interseismic deformation provide constraints on the partitioning of fault slip across plate boundary zones, the spatial distribution of both elastic and inelastic strain accumulation, and the nature of the fault system evolution. Here we describe linear block theory, which decomposes surface velocity fields into four components: (1) plate rotations, (2) elastic deformation from faults with kinematically consistent slip rates, (3) elastic deformation from faults with spatially variable coupling, and (4) homogeneous intrablock strain. Elastic deformation rates are computed for each fault segment in a homogeneous elastic half-space using multiple optimal planar Cartesian coordinate systems to minimize areal distortion and triangular dislocation elements to accurately represent complex fault system geometry. Block motions, fault-slip rates, elastic coupling, and internal block strain rates are determined simultaneously using a linear estimator with constraints from both geodetically determined velocity fields and geologic fault-slip rate estimates. We also introduce algorithms for efficiently implementing alternative fault-network geometries to quantify parameter sensitivity to nonlinear perturbations in model geometry.

We examine interseismic coupling of the Manila subduction zone and fault activity in the Luzon area using a block model constrained by GPS data collected from 1998 to 2015. Estimated long‐term slip rates along the Manila subduction zone show a gradual southward decrease from 90–100 mm/yr at the northwest tip of Luzon to 65–80 mm/yr at the southern portion of the Manila Trench. We provide two block models (models A and B) to illustrate possible realizations of coupling along the Manila Trench, which may be used to infer future earthquake rupture scenarios. Model A shows a low coupling ratio of 0.34 offshore western Luzon and continuous creeping on the plate interface at latitudes 18–19°N. Model B includes the North Luzon Trough Fault and shows prevalent coupling on the plate interface with a coupling ratio of 0.48. Both models fit GPS velocities well, although they have significantly different tectonic implications. The accumulated strain along the Manila subduction zone at latitudes 15–19°N could be balanced by earthquakes with composite magnitudes of Mw 8.8–9.2, assuming recurrence intervals of 500–1000 years. GPS observations are consistent with full locking of the majority of active faults in Luzon to a depth of 20 km. Inferred moments of large inland earthquakes in Luzon fall in the range of Mw 6.9–7.6 assuming a recurrence interval of 100 years.

1 Spatial patterns of interplate coupling on global subduction zones can be used to 2 guide seismic hazard assessment, but estimates of coupling are often constrained using a 3 limited temporal range of geodetic data. Here we analyze ~19 years of geodetic 4 observations from the GEONET network to assess time-dependent variations in the 5 spatial distribution of coupling on the subduction zones offshore Japan. We divide the 6 position time series into five, ~3.75-year epochs each decomposed into best-fit velocity, 7 annual periodic signals, coseismic offsets, and postseismic effects following five major 8 earthquakes. Nominally interseismic velocities are interpreted in terms of a combination 9 tectonic block motions and earthquake cycle activity. The duration of the inferred 10 postseismic activity covaries with the linear velocity. To address this trade-off, we 11 assume that the nominally interseismic velocity at each station varies minimally from 12 epoch to epoch. This approach is distinct from prior time-series analysis across the 13 earthquake cycle in that position data are not detrended using preseismic velocity, which 14 inherently assumes that interseismic processes are spatially stable through time, but rather 15 the best-fit velocity at each station may vary between epochs. These velocities reveal 16 significant consistency since 1996 in the spatial distribution of coupling on the Nankai 17 subduction zone, with variation limited primarily to the Tokai and Bungo Channel 18 regions, where long-term slow slip events have occurred, and persistently coupled 19 regions coincident with areas that slipped during historic great earthquakes. On the 20 Sagami subduction zone south of Tokyo, we also estimate relatively stable coupling 21 through time. On the Japan-Kuril Trench, we image significant coupling variations owing 22 combination of linear, periodic, step, and exponential functions, which we interpret to 58 represent nominally interseismic deformation related to earthquake cycle processes on the 59 subduction zones and crustal faults, seasonal effects, offsets due to earthquakes and 60 equipment maintenance, and postseismic deformation following large earthquakes, 61 respectively. We use the linear velocity fields as constraints on quasi-static elastic block 62 models, which provide a means for interpreting geodetic observations resulting from the 63 combined effects of tectonic block rotations, earthquake cycle processes (Meade and 64 Loveless, 2009), and volume changes of magma bodies. We use these models to image 65 patterns of subduction zone coupling in each of the five epochs, identifying persistently 66 coupled regions, effects of large earthquakes on subduction zone coupling, and the 67 occurrence of aseismic slip events. 68 Methods69 2.1. Decomposition of displacement time series 70We analyze F3 daily coordinates from the Geospatial Information Authority of Japan 71 during five time periods: April