Geodetic transients have been observed in various subduction zones. The 2011 Tohoku earthquake occurred in one of the most active subduction zones globally, the Japan Trench subduction zone (JTSZ). However, no geodetic transient (except afterslip and so on) had been reported in the JTSZ before the Tohoku earthquake. Here we show that a large transient event, with duration longer than any reported previously, occurred in the JTSZ preceding the Tohoku earthquake. We calculate tectonic deformations at Global Positioning System stations along the JTSZ by removing the effects of nearby M_w 6–8 earthquakes. We identify temporal changes in these deformations, deriving 9-year deviation records from regular deformations due to slip deficit at the plate boundary. We perform an inversion of the deviations to obtain the source model of their root event. The relationship between the obtained transient event and Tohoku earthquake is shown through Coulomb stress change and seismic supercycle simulation.

The ground motion and damage caused by the 2015 Gorkha, Nepal earthquake can be characterized by their widespread distributions to the east. Evidence from strong ground motions, regional acceleration duration, and teleseismic waveforms indicate that rupture directivity contributed significantly to these distributions. This phenomenon has been thought to occur only if a strike-slip or dip-slip rupture propagates to a site in the along-strike or updip direction, respectively. However, even though the earthquake was a dip-slip faulting event and its source fault strike was nearly eastward, evidence for rupture directivity is found in the eastward direction. Here, we explore the reasons for this apparent inconsistency by performing a joint source inversion of seismic and geodetic datasets, and conducting ground motion simulations. The results indicate that the earthquake occurred on the underthrusting Indian lithosphere, with a low dip angle, and that the fault rupture propagated in the along-strike direction at a velocity just slightly below the S-wave velocity. This low dip angle and fast rupture velocity produced rupture directivity in the along-strike direction, which caused widespread ground motion distribution and significant damage extending far eastwards, from central Nepal to Mount Everest.

The 2009 L'Aquila, Italy, earthquake (M_w 6.3) produced an unprecedented number of seismological records for a normal faulting event, and hence represents an important case study of damaging moderate magnitude earthquakes occurring in densely inhabited areas. We have investigated the source process of the 2009 L'Aquila earthquake in both the low- and broad-band frequency ranges by analysing the teleseismic and strong motion data. A low-frequency (<0.5 Hz) source model has been determined by waveform inversion of teleseismic and near-field strong motion data, yielding slip distributions with a major asperity located about 8 km southeast of the hypocentre. The broad-band (0.2–10 Hz) source characteristics were estimated using the empirical Green's function method providing the strong motion generation area of about 42 km² located southeast of the hypocentre below the village of Onna. This coincides with the location of the asperity from the inversion analysis, indicating that the low-frequency and broad-band ground motions produced during the earthquake were generated at similar locations on the fault plane. The position of the strong motion generation area also correlates well with the distribution of observed macroseismic (MCS) intensities reported by INGV. The maximum macroseismic intensities of IX–X were reported southeast of the epicentre, with an intensity of X measured in Onna. The source properties of the 2009 L'Aquila mainshock reveal the estimated size of the strong motion generation area to be in agreement with predictions made using empirical source scaling relation for inland crustal earthquakes, implying a stress drop of approximately 10 MPa. This further indicates that the 2009 L'Aquila earthquake involved a stress drop similar to that of previously recorded earthquakes in the Central and Southern Apennines.