We analyzed the acceleration time histories recorded by the K-NET and KiK-net stations of the M w 9 Tohoku Earthquake in order to investigate site response issues related to near-source effects. Time-frequency analysis of K-NET stations in the Miyagi prefecture, closest to the rupture area, show that sites having a V s30 < 400 m/s present a combination of deamplification at frequencies higher than 5 to 10 Hz and cyclic mobility (high acceleration peaks riding over a low frequency carrier). This suggests strong nonlinear site response at these stations. Furthermore, using KiK-net data we are able to compute borehole transfer functions from the mainshock and events having small PGA values from the local dataset. The ratio between weak-motion and strong-motion borehole transfer functions constitutes an indicator of nonlinear site response. This ratio reveals strong dependence on V s30 and shows that widespread nonlinear behavior took place during this large earthquake.

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The 2011 moment magnitude (M w ) 9.0 Tohoku-Oki Japan earthquake occurred in a region where giant megathrust earthquakes were not expected. This earthquake proved the difficulty in assessing seismic hazard by relying mainly on information from historical and instrumental seismicity. To help improve the seismic-hazard assessment for such rare events, we propose a methodology to estimate the slip distribution of future megathrust earthquakes based on a model of interseismic coupling distribution in subduction margins, as well as information of historical earthquakes, and apply the method to the central Peru region, Lima. The slip model obtained from geodetic data represents the large scale features of asperities within the megathrust, which is appropriate for simulation of long-period waves and tsunami modeling. For the simulation of a broadband strong ground motion, we add small scale heterogeneities to the source slip to be able to simulate high frequencies. To achieve this purpose, we propose broadband source models constructed by adding short-wavelength slip distributions obtained from a Von Karman power spectral density function, to the slip model inferred from interseismic geodetic data. Using these slip models and assuming several hypocenter locations, we calculate a set of strong ground motions for Lima and incorporate site effects obtained from microtremors surveys and geotechnical data. Our simulated average pseudospectral accelerations (period 0.3 s) are above 1:5g for wide areas in Lima, which may be critical in terms of damage of low-to midrise masonry and reinforced concrete buildings, which characterize the majority of buildings in Lima.

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Abstract.We propose a new procedure for estimating the critical slip weakening distance, Do, by evaluating the spatio-temporal distribution of the apparent stress calculated from the spatio-temporal distribution of the slip velocity function on the fault plane obtained from a kinematic inversion of the earthquake source. The idea is based on the fact that the apparent stress can be related to the difference between the earthquake average stress and the frictional dynamical stress on the fault plane during the rupture process. From the cumulative slip -apparent stress relationship we estimate the critical slip, Do, of the 1992 Landers earthquake. We find that the critical slip weakening plays an important role in controlling the rupture velocity. In the case of the Landers earthquake the very low rupture velocity in the central segment could be explained by the large D•-value obtained for the main asperity on that segment.

On 26 December 2004, a devastating earthquake of M 9.3 occurred offshore northern Sumatra. Due to the size of this earthquake and the accompanying tsunami wave, disastrous consequences have been observed in several countries around the Indian Ocean. The tectonics in the region are characterized by the oblique, north-northeast-oriented subduction of the Indian–Australian plate under the Sunda microplate with a rate of 6–6.5 cm/yr. This oblique convergence results in strain partitioning, where the trench-perpendicular thrust faulting along the subducting slab accommodates the east–west component of the motion, whereas the north–south component of the motion is probably accommodated by the right-lateral strike-slip faulting along the Great Sumatran fault and the Mentawi fault. Source parameters of the 26 December 2004 event have been used for modeling the resulting ground motions in the nearby affected regions. Results give an insight on the importance of ground shaking in the total destruction of places like Banda Aceh, northern Sumatra, Indonesia. The modeling is performed for a multiasperity finite fault using a hybrid procedure combining deterministic modeling at low frequencies and semistochastic modeling at high frequencies. Results show that strong shaking was distributed over a large area including northwestern Sumatra and its offshore islands. In Banda Aceh, which experienced significant damage, bedrock velocities reached 60 cm/sec with duration of the shaking of ca. 150 sec. The largest ground motions occurred near the strongest asperities of the fault plane, where velocities of 200 cm/sec are modeled for bedrock conditions.

We estimated the source process of the 2007/3/25 Notohanto earthquake using a new method for source imaging based on an "isochrones-backprojection" of observed seismograms in the source region (IBM). The IBM differs from conventional earthquake source modeling approaches in that no inversion procedures are required. The idea of IBM is to directly back-project amplitudes of seismogram envelopes around the source into a space image of the earthquake rupture. The method requires the calculation of isochrones times at every station used for source imaging, for a set of grids points distributed within the source fault plane. Total grid "brightness" is calculated by adding all observed waveform envelope amplitudes at every station, for every isochrone line crossing the grid, in order to produce an image of the total fault plane brightness distribution. Our source imaging results of the Notohanto earthquake show two large brightness regions; the first region is located 10 km above the hypocenter, and the second region is located at the bottom of the northern end of the fault plane. These regions approximately correspond to large slip areas obtained by a conventional inversion approach. Our method has the capability to quickly map asperities of large earthquakes using observed strong motion data.