S-wave velocity structure in the central Japan derived from adjoint tomography.

2021 ◽  
Author(s):  
Kota Mukumoto ◽  
Takeshi Tsuji
Keyword(s):  
Wave Velocity ◽  
Velocity Structure ◽  
Seismic Velocity ◽  
Philippine Sea Plate ◽  
S Wave ◽  
Low Velocity ◽  
Central Japan ◽  
Time Frequency ◽  
Adjoint Tomography ◽  
First Arrival

<p>In Japan, seismic velocity structures have been estimated by using first arrival tomography method. Many significant crustal structures such as the coordinate of the subducted Philippine Sea plate has been revealed by seismic tomographic images. In this study, we applied the adjoint tomography including full numerical simulation and finite frequency sensitivity kernels for the area of central Japan. The study area is characterized by the very heterogeneous geologic structures. We used 72 natural earthquakes in this study. Because the dominant phase used in our analysis is the surface wave, only S-wave velocity was inverted. We tried to minimize the time-frequency phase misfit between observed and calculated waveforms with the frequency of 0.033~0.1Hz. Based on the checker bord test, our inversion scenario resolved the upper and lower crust. From the results, we identified more heterogeneous structures compared to those from the first arrival tomography. The estimated S-wave velocity model clearly resolved the low velocity anomalies around the active volcanoes. Furthermore, the velocity boundaries agree with the main tectonic lines in the central Japan.</p>

Observation of Higher-Mode Surface Waves from an Active Source in the Hutubi Basin, Xinjiang, China

2021 ◽  
Author(s):  
Zhanbo Ji ◽  
Baoshan Wang ◽  
Wei Yang ◽  
Weitao Wang ◽  
Jinbo Su ◽  
...  
Keyword(s):  
Surface Waves ◽  
Wave Velocity ◽  
Seismic Waves ◽  
Velocity Structure ◽  
Group Velocity Dispersion ◽  
S Wave ◽  
Contributing Factors ◽  
Low Velocity ◽  
Time Frequency ◽  
Wave Modes

ABSTRACT Basins with thick sediments can amplify and prolong the incoming seismic waves, which may cause serious damage to surface facilities. The amplification of seismic energy depends on the shear-wave velocity of the uppermost layers, which is generally estimated through surface wave analysis. Surface waves may propagate in different modes, and the mechanism of the mode development is not well understood. Exploiting a recently deployed permanent airgun source in the Hutubi basin, Xinjiang, northwest China, we conducted a field experiment to investigate the development of multimode surface waves. We observed surface waves at the frequency of 0.3–5.0 Hz with apparent group velocities of 200–900  m/s, and identified five modes of surface waves (three Rayleigh-wave modes and two Love-wave modes) through time–frequency and particle-motion analyses. We then measured 125 group velocity dispersion curves of the fundamental- and higher-mode surface waves, and further inverted the 1D S-wave velocity structure of the Hutubi basin. The S-wave velocity increases abruptly from 238  m/s at the surface to 643  m/s at 300 m depth. Synthetic seismograms with the inverted velocity structure capture the main features of the surface waves of the different modes. Synthetic tests suggest that the low velocity, high velocity gradient, and shallow source depth are likely the dominant contributing factors in the development of higher-mode surface waves.

Mapping crustal structure of the Nechako–Chilcotin plateau using teleseismic receiver function analysis,

2014 ◽  
Vol 51 (4) ◽  
pp. 407-417 ◽  
Author(s):  
H.S. Kim ◽  
J.F. Cassidy ◽  
S.E. Dosso ◽  
H. Kao
Keyword(s):  
Wave Velocity ◽  
Crustal Structure ◽  
Velocity Structure ◽  
Receiver Function ◽  
Function Analysis ◽  
Crustal Thickness ◽  
Receiver Functions ◽  
S Wave ◽  
Low Velocity ◽  
Velocity Models

This paper presents results of a passive-source seismic mapping study in the Nechako–Chilcotin plateau of central British Columbia, with the ultimate goal of contributing to assessments of hydrocarbon and mineral potential of the region. For the present study, an array of nine seismic stations was deployed in 2006–2007 to sample a wide area of the Nechako–Chilcotin plateau. The specific goal was to map the thickness of the sediments and volcanic cover, and the overall crustal thickness and structural geometry beneath the study area. This study utilizes recordings of about 40 distant earthquakes from 2006 to 2008 to calculate receiver functions, and constructs S-wave velocity models for each station using the Neighbourhood Algorithm inversion. The surface sediments are found to range in thickness from about 0.8 to 2.7 km, and the underlying volcanic layer from 1.8 to 4.7 km. Both sediments and volcanic cover are thickest in the central portion of the study area. The crustal thickness ranges from 22 to 36 km, with an average crustal thickness of about 30–34 km. A consistent feature observed in this study is a low-velocity zone at the base of the crust. This study complements other recent studies in this area, including active-source seismic studies and magnetotelluric measurements, by providing site-specific images of the crustal structure down to the Moho and detailed constraints on the S-wave velocity structure.

UPPER MANTLE STRUCTURE IN CANADA FROM SEISMIC OBSERVATIONS USING CHEMICAL EXPLOSIONS

1967 ◽  
Vol 4 (5) ◽  
pp. 961-975 ◽  
Author(s):  
K. G. Barr
Keyword(s):  
Wave Velocity ◽  
Upper Mantle ◽  
Velocity Structure ◽  
P Wave ◽  
Hudson Bay ◽  
S Wave ◽  
Low Velocity ◽  
P Wave Velocity ◽  
Upper Mantle Structure ◽  
Chemical Explosions

Long-range seismic observations at the standard Canadian seismic stations, from chemical explosions in Hudson Bay and Lake Superior, are used to derive a P-wave velocity structure for the upper mantle. The coordinates of observed cusps are used to define the structural discontinuities. These discontinuities are at depths of 126 and 366 km, which agree closely with the depths of the S-wave velocity discontinuities deduced from surface-wave observations. The observations do not require a low velocity layer in the upper mantle.

P- and S-wave Velocity Structure beneath Central and East Java, Indonesia: Preliminary Result

2020 ◽  
Author(s):  
Faiz Muttaqy ◽  
Andri Dian Nugraha ◽  
Nanang T Puspito ◽  
James J Mori ◽  
Daryono Daryono ◽  
...  
Keyword(s):  
Wave Velocity ◽  
Velocity Structure ◽  
Tectonic Activity ◽  
Eurasian Plate ◽  
S Wave ◽  
Low Velocity ◽  
Slab Geometry ◽  
Tomographic Images ◽  
S Waves ◽  
Earthquake Zone

<p>The Central and East Java region is part of the Sunda Arc which has an important role in producing destructive earthquakes and volcanic complexes as a result of the subduction of the Indo-Australian plate under the Eurasian plate. Seismic tomography is one geophysical tool that is adaptable to understanding the mechanism process related to tectonic activity, seismicity, and volcanism. We collected a series of waveforms from 1,519 events in the period January 2009 to September 2017 and re-picked 11,192 phases for P- and S-waves at 34 stations of the BMKG network. We determined the 3-D P- and S-wave velocity structure beneath this high-risk region down to a depth of 200 km. In this study, we compare the tomographic images and relocated seismicity in order to represent the subducted slab geometry and the features in the seismic zones, i.e. the 2006 Yogyakarta earthquake zone (Opak fault), south of the mainland, and the 1994 Banyuwangi earthquake zone. Low-velocity anomalies beneath the volcanoes, i.e. Merapi, Merbabu, Kelud, Semeru, Bromo, and Ijen also imply the existence of fluid material and possible partial melting of the upper mantle which migrated from the subducted slab.</p>

scholarly journals Three-dimensional P and S Wave Velocity Structure beneath Central Japan.

2002 ◽  
Vol 53 (1) ◽  
pp. 1-28 ◽  
Author(s):  
Masaki Nakamura ◽  
Yasuhiro Yoshida ◽  
Dapeng Zhao ◽  
Kazumitsu Yoshikawa ◽  
Hiroyuki Takayama ◽  
...  
Keyword(s):  
Wave Velocity ◽  
Velocity Structure ◽  
Three Dimensional ◽  
S Wave ◽  
Central Japan

scholarly journals Spatial variation in coda Q around the Nobi fault zone, central Japan: relation to S-wave velocity and seismicity

2014 ◽  
Vol 66 (1) ◽  
Author(s):  
Sugane Tsuji ◽  
◽  
Yoshihiro Hiramatsu
Keyword(s):  
Spatial Variation ◽  
Fault Zone ◽  
Wave Velocity ◽  
S Wave ◽  
Coda Q ◽  
Central Japan

The relation between seismic P‐ and S‐wave velocity dispersion in saturated rocks

Geophysics ◽  
1994 ◽  
Vol 59 (1) ◽  
pp. 87-92 ◽  
Author(s):  
Gary Mavko ◽  
Diane Jizba
Keyword(s):  
Wave Velocity ◽  
Large Scale ◽  
Velocity Dispersion ◽  
Seismic Velocity ◽  
Ultrasonic Velocities ◽  
S Wave ◽  
Local Flow ◽  
Wave Velocities ◽  
Shear Compliance

Seismic velocity dispersionin fluid-saturated rocks appears to be dominated by tow mecahnisms: the large scale mechanism modeled by Biot, and the local flow or squirt mecahnism. The tow mechanisms can be distuinguished by the ratio of P-to S-wave dispersions, or more conbeniently, by the ratio of dynamic bulk to shear compliance dispersions derived from the wave velocities. Our formulation suggests that when local flow denominates, the dispersion of the shear compliance will be approximately 4/15 the dispersion of the compressibility. When the Biot mechanism dominates, the constant of proportionality is much smaller. Our examination of ultrasonic velocities from 40 sandstones and granites shows that most, but not all, of the samples were dominated by local flow dispersion, particularly at effective pressures below 40 MPa.

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