Volcanic eruptions are caused by the release of pressure that has accumulated due to hot volcanic fluids at depth. Here, we show extent regions affected pressurized can be imaged through measurement their response transient stress perturbations. We used records seismic noise from Japanese Hi-net network measure crustal velocity changes below 2011 moment magnitude (M(w)) 9.0 Tohoku-Oki earthquake. interpret coseismic reductions as related mechanical weakening crust dynamic associated with...

Abstract We present one of the first studies on source location determination for volcanic earthquakes and characterization subsurfaces using data from a distributed acoustic sensing (DAS) system. Using arrival time difference estimated well-correlated waveforms dense spatial distribution seismic amplitudes recorded along fiber-optic cable, we determine hypocenters at Azuma volcano, Japan. The sources are located shallow depth beneath active areas with range approximately 1 km. Spatial site...

Abstract Many unknowns exist regarding the energy radiation processes of intraplate low‐frequency earthquakes (LFEs), which are frequently observed beneath volcanoes. To evaluate their characteristics, we estimated scaled () for LFEs and regular around focal area 2008 6.9 Iwate‐Miyagi, Japan, earthquake. Their source spectra were first obtained by correcting site path effects from direct S‐waves. We then radiated seismic moment 1,421 earthquakes, 62 deep LFEs, 46 shallow LFEs. The is in...

SUMMARY The source characteristics of offshore seismic events, especially regular (or fast) and slow earthquakes, can provide key information on their physics frictional conditions at the plate boundary. Due to strong 3-D heterogeneities in regions, such as those relating sea water, accretionary prism small-scale velocity heterogeneity, conventional methods using a 1-D earth model may mis-estimate parameters duration radiation energy. Estimations could become severe inaccuracies for small...

Abstract We detected shallow very low frequency earthquakes (VLFEs) off the Cape Muroto and Kii Channel in Nankai subduction zone estimated their moment rate functions. Combining new previously catalogs, we obtained comprehensive catalog of VLFE functions along Trough. defined swarms investigated scaling relationships cumulative moments, activity area, durations each region. Detected were considered candidates for slow slip events. A similar relationship was observed between moments areas,...

Abstract To clarify the characteristics of high-frequency (> 1 Hz) S and -coda waves at ocean-bottom seismometers (OBSs), we analyzed seismograms observed permanent OBSs inland broadband around Kii Peninsula in southwest Japan along Nankai Trough. The coda amplitudes (both horizontal vertical) were much larger than those rock-site stations. Because relative to stations have been used as site-amplification factors, large site amplifications for both components can be expected due presence...

Abstract Estimating the radiated energy of small‐to‐moderate ( M w < 5) earthquakes remains challenging because their decay significantly during wave propagation. Even when near‐source records are available, seismic waves pass through shallow crust with strong attenuation, which can bias estimates. This study evaluated degree dissipation in modeling (<12 km) waveform data northern Ibaraki Prefecture, Japan. High‐quality waveforms recorded at a downhole sensor confined by granite high...

In short‐period seismograms of earthquakes, we often observe the broadening apparent duration P and/or S waves and excitation transverse component especially for as travel distance increases. Such phenomena are well explained by scattering caused random velocity fluctuation in lithosphere. The Markov approximation is known one powerful stochastic methods direct synthesis wave envelopes. We extend method to synthesize vector envelopes on free surface a medium since seismic observation usually...

Abstract Stress accumulation and release inside the plate remains poorly understood compared to that at boundaries. Spatiotemporal variations in foreshock aftershock activities can provide key constraints on time‐dependent stress deformation processes plate. The 2017 M 5.2 Akita‐Daisen intraplate earthquake NE Japan was preceded by intense activity triggered a strong sequence of aftershocks. We examine spatiotemporal distributions foreshocks aftershocks determine coseismic slip distribution...

SUMMARY The spatial autocorrelation (SPAC) method has been applied to ambient seismic noise measured by arrays of translational seismometers for inverting phase-velocity dispersion curves Rayleigh or Love waves shallow S-wave velocity structure. Recently, it is becoming possible observe wave gradients such as strain, rotation and tilt owing the development dense networks improving measurement technologies. Therefore, desirable extend formulation SPAC tilt. This study presents analytical...

Abstract We investigated the effects of propagation path and site amplification shallow tremors along Nankai Trough. Using far‐field S ‐wave from intraslab earthquake data, factors at DONET stations were 5–40 times against an inland outcrop rock site. Thick (∼5 km) sedimentary layers with V 0.6–2 km/s beneath have been confirmed by seismological studies. To investigate thick layers, we synthesized seismograms earthquakes seafloor stations. The ratios maximum amplitudes synthetic between...

In high-frequency seismograms of a small earthquake, coda waves continue for long time and the S-wavelet is broadened as travel distance increases. Those phenomena can be interpreted results scattering by random inhomogeneities distributed in solid earth. Recent measurements show that power spectrum medium heterogeneities decreases according to some wavenumber. As mathematical model, we study propagation scalar wavelet through von Kármán-type media. Our objective propose stochastic method...

Short-period (<1 s) seismograms are strongly affected by small-scale (<10 km) heterogeneities in the lithosphere. In general, short-period analysed based on statistical method considering interaction between seismic waves and randomly distributed heterogeneities. Statistical properties of random have been estimated analysing seismograms. However, generally, heterogeneity is not taken into account for modelling long-period (>2 We found that energy coda shows a spatially flat distribution....

The Markov approximation is a powerful stochastic method for the direct synthesis of wave envelopes in random velocity fluctuated media when wavelength shorter than their correlation distance. To apply to realistic cases, we consider horizontal layered characterized by an anisotropic autocorrelation function (ACF), where different layers have randomnesses and background velocities having step-like changes. Solving parabolic master equation two frequency mutual coherence (TFMCF) elastic...

Random velocity fluctuations distributed in the solid Earth function as sources of seismic wave scattering. Scattering effects are often observed high-frequency seismograms earthquakes broadening apparent duration an S-wavelet and emergence coda waves. We conduct large-scale 3-D finite difference (FD) simulations scalar equation to analyse intensities scattered waves propagating through random small-scale heterogeneous media. First, we compare ensemble averaged (mean square amplitudes)...

In high-frequency seismograms of small earthquakes, we clearly see the excitation long lasting coda waves and envelope broadening an S-wavelet with travel distance increasing. We can interpret those phenomena resulting from scattering by random inhomogeneities distributed in earth medium. Those have been theoretically studied stochastic methods, which deal velocity as media. As a simple mathematical model, study propagation scalar wavelet for spherical radiation point source 3-D von...

SUMMARY For the study of random velocity fluctuation solid Earth medium, it is useful to measure collapse a seismic wavelet with increasing travel distance and excitation coda waves. Radiative transfer theory (RTT) powerful tool for synthesizing propagation in media statistically characterized by power spectral density function (PSDF) fractional fluctuation. The Born scattering coefficient key building block RTT. As centre wavenumber increases, phase shift across correlation length increases...

In the heterogeneous earth medium, short period seismograms of an earthquake are well characterized by their smooth envelopes with random phases. The Markov approximation has often been used for practical synthesis a given frequency band. It is stochastic extension phase screen method to synthesize wave in media fluctuations under condition that wavelength shorter than correlation distance fluctuation. We propose envelope case isotropically outgoing wavelet radiated from point source...

We investigated the effects of propagation path and site amplification shallow tremors along Nankai Trough. Using far-field S-wave from intraslab earthquake data, factors at DONET stations were 5–40 times against an inland outcrop rock site. Thick (~5 km) sedimentary layers with VS 0.6–2 km/s beneath have been confirmed by seismological studies. To investigate thick layers, we synthesized seismograms earthquakes seafloor stations. The ratios maximum amplitudes synthetic between models...