Aitaro Kato

Many large earthquakes are preceded by one or more foreshocks, but it is unclear how these foreshocks relate to the nucleation process of the mainshock. On the basis of an earthquake catalog created using a waveform correlation technique, we identified two distinct sequences of foreshocks migrating at rates of 2 to 10 kilometers per day along the trench axis toward the epicenter of the 2011 moment magnitude (M(w)) 9.0 Tohoku-Oki earthquake in Japan. The time history of quasi-static slip along th

We show fine‐scale variations of seismic velocities and converted teleseismic waves that reveal the presence of zones of high‐pressure fluids released by progressive metamorphic dehydration reactions in the subducting Philippine Sea plate in Tokai district, Japan. These zones have a strong correlation with the distribution of slow earthquakes, including long‐term slow slip (LTSS) and low‐frequency earthquakes (LFEs). Overpressured fluids in the LTSS region appear to be trapped within the oceanic

We here show relocated hypocenters within a seismic sequence with normal faults in the northern part of Ibaraki Prefecture, triggered after the M 9.0 2011 off the Pacific coast of Tohoku Earthquake. Depth-sections of the hypocenters from the center of the northern Ibaraki region to the north show an earthquake alignment dipping westwards at 40° to 50° at depths shallower than 10 km. On the other hand, hypocenters from the center to the south show a cross-cutting geometry consisting of conjugate

Abstract To obtain a precise record of the foreshock sequence before the 2014 Iquique, Chile M w 8.1 earthquake, we applied a matched filter technique to continuous seismograms recorded near the source region. We newly detected about 10 times the number of seismic events listed in the routinely constructed earthquake catalog and identified multiple sequences of earthquake migrations at speeds of 2–10 km/d, both along strike and downdip on the fault plane, updip of the main shock area. In additio

We analyzed seismicity linked to the 2014 phreatic eruption of Mount Ontake, Japan, on 27 September 2014. We first relocated shallow volcano tectonic (VT) earthquakes and long-period (LP) events from August to September 2014. By applying a matched-filter technique to continuous waveforms using these relocated earthquakes, we detected numerous additional micro-earthquakes beneath the craters. The relocated VT earthquakes aligned on a near-vertical plane oriented NNW–SSE, suggesting they occurred

The earthquake nucleation process has been vigorously investigated based on geophysical observations, laboratory experiments, and theoretical studies; however, a general consensus has yet to be achieved. Here, we studied nucleation process for the 2014 Iquique, Chile Mw 8.2 megathrust earthquake located within the current North Chile seismic gap, by analyzing a long-term earthquake catalog constructed from a cross-correlation detector using continuous seismic data. Accelerations in seismicity, t

Since the 2011 Tohoku‐Oki earthquake, many fault source models have been constructed using a variety of data, such as teleseismic, strong ground motion, geodetic, and tsunami recordings. However, questions remain as to how far the associated large‐slip zone extended along the plate interface during the rupture. Here we delineate the outer edge of this large‐slip zone in detail, based on the sharp density contrast observed for interplate, repeating, and down‐dip compressional earthquakes induced

Abstract The M j 6.5 ( M w 6.2) event that occurred on 5 May 2023 near the northern shoreline of the northeastern tip of the Noto Peninsula, central Japan, is the largest event to date in a long‐lasting, intense earthquake swarm. Here we have created a more precise aftershock catalog associated with the 2023 M j 6.5 and the second‐largest 2022 M j 5.4 sequence to understand the rupture process of this largest earthquake. Most of the aftershocks are aligned along a ∼45° SE‐dipping plane. The main

The velocity structure and accurate aftershock distributions of the 2004 mid‐Niigata prefecture earthquake are elucidated by inverting the arrival times from 716 aftershocks using double‐difference tomography. Fourteen temporal seismic stations were immediately deployed in and around the source region within 46 h of the occurrence of mainshock. The seismic velocities in a hanging wall are lower than those in a footwall, and the velocity contrast extends to a depth of approximately 10 km. The aft

Large historical and recent intraplate earthquakes have been concentrated along a contractional zone at the eastern margin of the Japan Sea back‐arc basin. Here we present high‐resolution three‐dimensional tomographic imaging of seismic velocities in this zone using data from a dense seismograph deployment. We discover that stepwise and tilted block structures of the basement, which are geophysical evidence of a Miocene rift system, are widely distributed beneath the thick sedimentary basin. Mos

Seismic data reveal that the aftershock zone expands with time after a main shock event. Here we examine the aftershock sequence recorded during the first 32 days following the 2007 Noto-Hanto earthquake, Japan. By applying a matched-filter technique to the data, we detected about 10 times more events than those listed in the routinely constructed earthquake catalog. The aftershock area expanded along the fault strike as a logarithmic function of time, beginning immediately after the main shock.

We deployed a dense temporal seismic network in the source region of the 2004 mid‐Niigata prefecture earthquake (thrust fault), Japan. A detailed velocity structure and accurate aftershock distributions were elucidated by inverting aftershock arrival times using double‐difference tomography. A stress tensor inversion using the first‐motion data was also conducted in order to investigate the stress field. The seismic velocities in the hanging wall above the main shock fault are lower than those i

Beginning in April 2016, a series of shallow, moderate to large earthquakes with associated strong aftershocks struck the Kumamoto area of Kyushu, SW Japan. An M_j 7.3 mainshock occurred on 16 April 2016, close to the epicenter of an M_j 6.5 foreshock that occurred about 28 hours earlier. The intense seismicity released the accumulated elastic energy by right-lateral strike slip, mainly along two known, active faults. The mainshock rupture propagated along multiple fault segm

Abstract To improve our understanding of the long-term behavior of low-frequency earthquakes (LFEs) along the tremor belt of the Nankai subduction zone, we applied a matched filter technique to continuous seismic data recorded by a dense and highly sensitive seismic network over an 11-year window, April 2004 to August 2015. We detected a total of ~ 510,000 LFEs, or ~ 23 × the number of LFEs in the JMA catalog for the same period. During long-term slow slip events (SSEs) in the Bungo Channel, a s