Satoshi Ide

Strong spatial variation of rupture characteristics in the moment magnitude (M(w)) 9.0 Tohoku-Oki megathrust earthquake controlled both the strength of shaking and the size of the tsunami that followed. Finite-source imaging reveals that the rupture consisted of a small initial phase, deep rupture for up to 40 seconds, extensive shallow rupture at 60 to 70 seconds, and continuing deep rupture lasting more than 100 seconds. A combination of a shallow dipping fault and a compliant hanging wall may

Seismic energy is distributed across a wide frequency band so that limited bandwidth recording can lead to substantial underestimates of the radiated seismic energy or introduce an artificial upper bound of radiated energy. We estimate an adjustment factor to account for the probable missing energy and apply it to three previously studied data sets with limited recording bandwidth. We find that this adjustment, together with accounting for possibly missing events, eliminates much of the moment d

Constitutive laws define the boundary conditions on fault plane and govern many aspects of earthquake failure. Although several constitutive laws have been formulated based on laboratory rock experiments and applied to theoretical studies in various fields, no actual relation during a natural earthquake has been determined. The 1995 Kobe earthquake is suitable for detailed kinematic analysis, and this enables the first evaluation of constitutive relations for a natural earthquake. In this study,

We study the mechanism of low frequency earthquakes (LFEs) in the Nankai Trough in western Shikoku, Japan. Precise locations have previously suggested that they represent shear slip on the plate boundary. In this paper we examine the mechanism of these events. Due to the low signal‐to‐noise ratio, we analyze stacked LFE waveforms and compare them with the waveforms of nearby earthquakes of known mechanism within the subducting Philippine Sea Plate. Analysis of both the focal mechanism using P ‐w

We reexamine the scaling of stress drop and apparent stress, rigidity times the ratio between seismically radiated energy to seismic moment, with earthquake size for a set of microearthquakes recorded in a deep borehole in Long Valley, California. In the first set of calculations, we assume a constant Q and solve for the corner frequency and seismic moment. In the second set of calculations, we model the spectral ratio of nearby events to determine the same quantities. We find that the spectral

Deep tectonic tremor occurs at various sites worldwide, and the source characteristics are heterogeneous, even at small scales. In this study, tremor sources were determined using data sets of seismic waveforms from various locations, some of which are not well recognized as being a site of tremor activity. The regions of interest are subduction zones at Nankai and Kyushu, Japan, Cascadia in western North America, Mexico, southern Chile, and New Zealand. Tremor locations are consistent with the

We propose a model of the wide‐scale growth of dynamic rupture during an earthquake, based on our multiscale simulation of a planar crack in a three‐dimensional homogeneous elastic space. A simple slip‐weakening law governs the fracture/friction processes, and its characteristic parameters, slip‐weakening distance and fracture surface energy, have multiscale heterogeneous distributions. We consider a set of randomly distributed circular patches, whose diameter is proportional to the fracture sur

Abstract The Kobe (Hyogo-ken Nanbu) earthquake (MS 6.8) occurred on 16 January 1995, in western Japan, bringing about a tremendous disaster. We constructed its source model by determining a spatio-temporal slip distribution using strong-motion seismograms recorded at a number of stations near the hypocenter. The source area is expressed using both a rough and a detailed subfault discretization system and a source-time function expanded with a finite number of basis functions at each subfault is

Recently observed unusual seismic events: deep low frequency earthquakes and tremor, very low frequency earthquakes, and slow slip events form a family of slow earthquakes that are governed by a scaling law different from ordinary earthquakes. Guided by this scaling law, we have observed previously unknown events, with source duration of 20–200 s and moment magnitude of 3–4, under the Kii Peninsula in western Japan. These events radiate seismic energy in the 2–8 Hz band in direct proportion to t

Along some subduction plate boundaries, slow deformation is observable as seismically detected deep low‐frequency tremor and geodetically detected slow slip events. These phenomena are considered as different manifestations of slow earthquakes characterized by fairly constant seismic moment rate. This paper presents a simple model of slow earthquakes that can explain wide variety of observed features including the steady moment rate and scaled energy, characteristics of tremor signals both in ti

Abstract Deep tectonic tremors have been observed together with signals in the very low frequency (VLF) band from 0.02 to 0.05 Hz, which have been identified as VLF events in limited regions of subduction zones. By stacking broadband seismograms relative to the timing of tremors, we have detected similar signals in all regions where tremors occur in western Japan. These signals are inverted to obtain the moment tensor, and the fault‐normal and slip vectors are generally consistent with the geome

A large, Ms = 7.2, shallow earthquake took place off the Pacific coast of Nicaragua on September 2, 1992, and set off large tsunamis. The ground motion of the main shock was very weak along the whole Nicaraguan coast. A tsunami as high as 10 m was observed at El Transito, whereas a height of about 2 m is empirically expected for an earthquake of Ms 7.2. The tsunami magnitude Mt is estimated to be 7.9 from tide gage data. The Nicaraguan event is a tsunami earthquake which generates unusually larg