SUMMARY A network of 27 GPS sites was implemented in Iran and northern Oman to measure displacements in this part of the Alpine–Himalayan mountain belt. We present and interpret the results of two surveys performed in 1999 September and 2001 October. GPS sites in Oman show northward motion of the Arabian Plate relative to Eurasia slower than the NUVEL‐1A estimates (e.g. 22 ± 2 mm yr−1 at N8°± 5°E instead of 30.5 mm yr−1 at N6°E at Bahrain longitude). We define a GPS Arabia–Eurasia Euler vector of 27.9°± 0.5°N, 19.5°± 1.4°E, 0.41°± 0.1° Myr−1. The Arabia–Eurasia convergence is accommodated differently in eastern and western Iran. East of 58°E, most of the shortening is accommodated by the Makran subduction zone (19.5 ± 2 mm yr−1) and less by the Kopet‐Dag (6.5 ± 2 mm yr−1). West of 58°E, the deformation is distributed in separate fold and thrust belts. At the longitude of Tehran, the Zagros and the Alborz mountain ranges accommodate 6.5 ± 2 mm yr−1 and 8 ± 2 mm yr−1 respectively. The right‐lateral displacement along the Main Recent Fault in the northern Zagros is about 3 ± 2 mm yr−1, smaller than what was generally expected. By contrast, large right‐lateral displacement takes place in northwestern Iran (up to 8 ± mm yr−1). The Central Iranian Block is characterized by coherent plate motion (internal deformation <2 mm yr−1). Sites east of 61°E show very low displacements relative to Eurasia. The kinematic contrast between eastern and western Iran is accommodated by strike‐slip motions along the Lut Block. To the south, the transition zone between Zagros and Makran is under transpression with right‐lateral displacements of 11 ± 2 mm yr−1.

A unique GPS velocity field that spans the entire Southeast Asia region is presented. It is based on 10 years (1994–2004) of GPS data at more than 100 sites in Indonesia, Malaysia, Thailand, Myanmar, the Philippines, and Vietnam. The majority of the horizontal velocity vectors have a demonstrated global accuracy of ∼1 mm/yr (at 95% confidence level). The results have been used to (better) characterize the Sundaland block boundaries and to derive a new geokinematic model for the region. The rotation pole of the undeformed core of the Sundaland block is located at 49.0°N–94.2°E, with a clockwise rotation rate of 0.34°/Myr. With respect to both geodetically and geophysically defined Eurasia plate models, Sundaland moves eastward at a velocity of 6 ± 1 to 10 ± 1 mm/yr from south to north, respectively. Contrary to previous studies, Sundaland is shown to move independently with respect to South China, the eastern part of Java, the island of Sulawesi, and the northern tip of Borneo. The Red River fault in South China and Vietnam is still active and accommodates a strike‐slip motion of ∼2 mm/yr. Although Sundaland internal deformation is general very small (less than 7 nanostrain/yr), important accumulation of elastic deformation occurs along its boundaries with fast‐moving neighboring plates. In particular in northern Sumatra and Malaysia, inland‐pointing trench‐perpendicular residual velocities were detected prior to the megathrust earthquake of 26 December 2004. Earlier studies in Sumatra already showed this but underestimated the extent of the deformation zone, which reaches more than 600 km away from the trench. This study shows that only a regional Southeast Asia network spanning thousands of kilometers can provide a reference frame solid enough to analyze intraplate and interplate deformation in detail.

The subduction zone in northern Chile is a well-identified seismic gap that last ruptured in 1877. The moment magnitude (Mw) 8.1 Iquique earthquake of 1 April 2014 broke a highly coupled portion of this gap. To understand the seismicity preceding this event, we studied the location and mechanisms of the foreshocks and computed Global Positioning System (GPS) time series at stations located on shore. Seismicity off the coast of Iquique started to increase in January 2014. After 16 March, several Mw > 6 events occurred near the low-coupled zone. These events migrated northward for ~50 kilometers until the 1 April earthquake occurred. On 16 March, on-shore continuous GPS stations detected a westward motion that we model as a slow slip event situated in the same area where the mainshock occurred.

No abstract

Data collected at approximately 60 Global Positioning System (GPS) sites in southeast Asia show the crustal deformation caused by the 26 December 2004 Sumatra-Andaman earthquake at an unprecedented large scale. Small but significant co-seismic jumps are clearly detected more than 3,000 km from the earthquake epicentre. The nearest sites, still more than 400 km away, show displacements of 10 cm or more. Here we show that the rupture plane for this earthquake must have been at least 1,000 km long and that non-homogeneous slip is required to fit the large displacement gradients revealed by the GPS measurements. Our kinematic analysis of the GPS recordings indicates that the centroid of released deformation is located at least 200 km north of the seismological epicentre. It also provides evidence that the rupture propagated northward sufficiently fast for stations in northern Thailand to have reached their final positions less than 10 min after the earthquake, hence ruling out the hypothesis of a silent slow aseismic rupture.

The recent expansion of dense GPS networks over plate boundaries allows for remarkably precise mapping of interseismic coupling along active faults. The interseismic coupling coefficient is related to the ratio between slipping velocity on the fault during the interseismic period and the long-term plates velocity, but the interpretation of coupling in terms of mechanical behaviour of the fault is still unclear. Here, we investigate the link between coupling and seismicity over the Chilean subduction zone that ruptured three times in the last 5 years with major earthquakes (

[1] Using a regional GPS data set including $190 stations in Asia, from Nepal to eastern Indonesia and spanning 11 years, we update the present-day relative motion between the Indian and Sundaland plates and discuss the deformation taking place between them in Myanmar. Revisiting measurements acquired on the Main Boundary Thrust in Nepal, it appears that points in southern Nepal exhibit negligible deformation with respect to mainland India. Including these points, using a longer time span than previous studies, and making an accurate geodetic mapping in the newest reference frame allows us to refine the present-day Indian motion. Our results confirm that the current motion of India is slower than predicted by the NUVEL-1A model, and in addition our India-Eurasia motion is significantly ($5 mm/yr) slower than previous geodetic determinations. This new Indian motion, combined with a refined determination of the Sundaland motion, gives way to a relative India-Sunda angular velocity of 20.2°N, 26.1°E, 0.370°/Myr in ITRF2000, predicting a relative motion of 35 mm/yr oriented N10°at the latitude of Myanmar. There, the Sagaing Fault accommodates only 18 mm/yr of right-lateral strike slip, only half of the shear component of motion. We present two models addressing how and where the remaining deformation may occur. A first model of distributed deformation implies convergence on the Arakan subduction (the northern continuation of the now famous Sumatra-Andaman Trench) and wrench faulting in the Arakan wedge. The second model uses localized deformation, where deformation observed west of the Sagaing Fault is entirely due to elastic loading on a faster and oblique Arakan subduction (23 mm/yr). This latter model predicts that a major earthquake of M w 8.5 may occur every century on this segment of the subduction.

[1] Global Positioning System (GPS) measurements carried out in Chile over the last two decades showed that an entire portion of the Nazca-South America subduction zone (38°S À 24°S) was locked over this period of time. The induced accumulation of elastic deformation in the upper-plate was not released until the recent Maule earthquake of 27 February 2010 (M w 8.8) that ruptured the southern part of this section. Locking or coupling between the two plates varies both with depth and along strike. Here we use our own GPS data (an updated solution of our extended network in central Chile), combined with other published data sets, to quantify the spatial variations of the coupling that prevailed before the Maule earthquake. Using a simple elastic model based on the back-slip assumption, we show that coupling variations on the subduction plane are sufficient to explain the observed surface deformation, with no need of a sliver in central Chile. We identify four segments characterized by higher coupling and separated by narrow areas of lower coupling. This segmentation is in good agreement with historical and recent seismicity in Chile. In particular the narrow zones of lower coupling seem to have stopped most large seismic ruptures, including Maule's. These zones are often associated with irregular bathymetric or coastal features (fracture zones or peninsulas). Finally, coseismic and early post-seismic slip distribution of the Maule earthquake, occurring either in previously highly or weakly coupled zones, map a complex distribution of velocity-weakening and velocity-strengthening patches on the subduction interface.