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The two largest earthquakes of the past 40 years ruptured a 1600-kilometer-long portion of the fault boundary between the Indo-Australian and southeastern Eurasian plates on 26 December 2004 [seismic moment magnitude ([M.sub.w]) = 9.1 to 9.3] and 28 March 2005 ([M.sub.w] = 8.6). The first event generated a tsunami that caused more than 283,000 deaths. Fault slip of up to 15 meters occurred near Banda Aceh, Sumatra, but to the north, along the Nicobar and Andaman Islands, rapid slip was much smaller. Tsunami and geodetic observations indicate that additional slow slip occurred in the north over a time scale of 50 minutes or longer., The 26 December 2004 Sumatra-Andaman earthquake was the largest seismic event on Earth in more than 40 years, and it produced the most devastating tsunami in recorded history (1). Like [...]

Author(s): Rachel E. Abercrombie (corresponding author); Göran Ekström Oceanic transform faults are one of the main types of plate boundary, but the manner in which they slip remains poorly understood. [...]

Tomographic models of the Earth's mantle usually assume that fast and slow seismic velocity anomalies represent a spatially heterogeneous temperature field linked with mantle convection. A global three-dimensional tomographic model of shear-wave velocity is presented, showing that the uppermost mantle below the central Pacific Ocean is considerably complex. Regional anomalies in elastic anisotropy are revealed, producing seismic velocity variations.

Most earthquakes follow a simple scaling relationship such that the duration of fault movement is proportional to [10.sup.M/2], where M is the earthquake moment magnitude. The typical duration of an [...], We have detected dozens of previously unknown, moderate earthquakes beneath large glaciers. The seismic radiation from these earthquakes is depleted at high frequencies, explaining their nondetection by traditional methods. Inverse modeling of the long-period seismic waveforms from the best-recorded earthquake, in southern Alaska, shows that the seismic source is well represented by stick-slip, downhill sliding of a glacial ice mass. The duration of sliding in the Alaska earthquake is 30 to 60 seconds, about 15 to 30 times longer than for a regular tectonic earthquake of similar magnitude.

A large portion of geoscience efforts is directed toward understanding the properties of earthquakes to improve the techniques for earthquake prediction. The 1995 earthquakes in Kobe, Japan, and Neftogorsk, Russia, provide evidence of the need for more developments in earthquake research. Over the past decade, the discipline of earthquake seismology has achieved significant progress toward this direction. Some of the important developments were the establishment of about 90 permanent and 300 portable broadband digital seismographic stations around the world and evidence of aftershocks and fault behavior.

We develop an approach that allows us to invert for the mantle velocity structure within a finely parametrized region as a perturbation with respect to a low-resolution, global tomographic model. We implement this technique to investigate the upper-mantle structure beneath Eurasia and present a new model of shear wave velocity, parametrized laterally using spherical splines with similar to 2.9 degrees spacing in Eurasia and similar to 11.5 degrees spacing elsewhere. The model is obtained from a combined data set of surface wave phase velocities, long-period waveforms and body-wave traveltimes. We identify many features as narrow as few hundred kilometres in diameter, such as subducting slabs in eastern Eurasia and slow-velocity anomalies beneath tectonically active regions. In contrast to regional studies in which these features have been identified, our model encompasses the structure of the entire Eurasian continent. Furthermore, including mantle- and body-wave waveforms helped us constrain structures at depths larger than 250 km, which are poorly resolved in earlier models. We find that up to +9 per cent faster-than-average anomalies within the uppermost similar to 200 km of the mantle beneath cratons and some orogenic regions are separated by a sharp gradient zone from deeper, +1 to +2 per cent anomalies. We speculate that this gradient zone may represent a boundary separating the lithosphere from the continental root, which might be compositionally distinct from the overlying lithosphere and remain stable either due to its compositional buoyancy or due to higher viscosity compared with the suboceanic mantle. Our regional model of anisotropy is not significantly different from the global one., Earth and Planetary Sciences