scholarly journals Last stage of the Japan Sea back-arc opening deduced from the seismic velocity structure using wide-angle data

2006 ◽  
Vol 7 (6) ◽  
pp. n/a-n/a ◽  
Author(s):  
Takeshi Sato ◽  
Narumi Takahashi ◽  
Seiichi Miura ◽  
Gou Fujie ◽  
Dong-Hyo Kang ◽  
...  
Keyword(s):  
Velocity Structure ◽  
Seismic Velocity ◽  
Japan Sea ◽  
Wide Angle ◽  
Seismic Velocity Structure ◽  
Angle Data ◽  
The Japan Sea ◽  
Last Stage ◽  
Back Arc

Slowness‐weighted diffraction stack for migrating wide‐angle seismic data in laterally varying media

Geophysics ◽  
2004 ◽  
Vol 69 (4) ◽  
pp. 1046-1052 ◽  
Author(s):  
Harm J. A. Van Avendonk
Keyword(s):  
Seismic Data ◽  
Velocity Structure ◽  
Seismic Velocity ◽  
Image Space ◽  
Wide Angle ◽  
Data Set ◽  
Seismic Velocity Structure ◽  
Depth Migration ◽  
Angle Data ◽  
Reflecting Boundaries

Wide‐angle prestack depth migration is an important tool for studying the nature of reflecting boundaries in the earth's crust. The slowness‐weighted diffraction stack (SWDS) method has been used to incorporate both two‐way traveltime constraints and slowness information in the migration. For this purpose, traveltimes and apparent slownesses of reflected arrivals must be calculated in the image space. Earlier applications of SWDS required a 1D or gently varying seismic velocity structure to obtain these quantities by ray tracing in the image space. I show that the apparent slownesses can also be derived directly from one‐way traveltime maps using Fermat's principle. The SDWS is applied to an existing onshore–offshore wide‐angle data set, and the example shows that the method can be used to image detailed reflectivity structure at great depths.

scholarly journals Seismic Velocity Structure of Kita-Yamato Trough, Japan Sea Revealed by Ocean Bottom Seismometer and Airgun Survey

2001 ◽  
Vol 53 (4) ◽  
pp. 337-355 ◽  
Author(s):  
Takeshi SATO ◽  
Masanao SHINOHARA ◽  
Kiyoshi SUYEHIRO ◽  
Nobuhiro ISEZAKI ◽  
Boris Y. KARP ◽  
...  
Keyword(s):  
Velocity Structure ◽  
Seismic Velocity ◽  
Japan Sea ◽  
Ocean Bottom ◽  
Ocean Bottom Seismometer ◽  
Seismic Velocity Structure

scholarly journals Seismic velocity structure at the southern termination of the 2016 Kumamoto Earthquake rupture, Japan

2020 ◽  
Vol 72 (1) ◽  
Author(s):  
Yasuhira Aoyagi ◽  
Haruo Kimura ◽  
Kazuo Mizoguchi
Keyword(s):  
Fault Zone ◽  
Velocity Structure ◽  
Seismic Velocity ◽  
Earthquake Rupture ◽  
2016 Kumamoto Earthquake ◽  
Seismic Velocity Structure ◽  
Kumamoto Earthquake ◽  
Seismogenic Layer ◽  
The 2016 Kumamoto Earthquake ◽  
Tectonic Line

Abstract The earthquake rupture termination mechanism and size of the ruptured area are crucial parameters for earthquake magnitude estimations and seismic hazard assessments. The 2016 Mw 7.0 Kumamoto Earthquake, central Kyushu, Japan, ruptured a 34-km-long area along previously recognized active faults, eastern part of the Futagawa fault zone and northernmost part of the Hinagu fault zone. Many researchers have suggested that a magma chamber under Aso Volcano terminated the eastward rupture. However, the termination mechanism of the southward rupture has remained unclear. Here, we conduct a local seismic tomographic inversion using a dense temporary seismic network to detail the seismic velocity structure around the southern termination of the rupture. The compressional-wave velocity (Vp) results and compressional- to shear-wave velocity (Vp/Vs) structure indicate several E–W- and ENE–WSW-trending zonal anomalies in the upper to middle crust. These zonal anomalies may reflect regional geological structures that follow the same trends as the Oita–Kumamoto Tectonic Line and Usuki–Yatsushiro Tectonic Line. While the 2016 Kumamoto Earthquake rupture mainly propagated through a low-Vp/Vs area (1.62–1.74) along the Hinagu fault zone, the southern termination of the earthquake at the focal depth of the mainshock is adjacent to a 3-km-diameter high-Vp/Vs body. There is a rapid 5-km step in the depth of the seismogenic layer across the E–W-trending velocity boundary between the low- and high-Vp/Vs areas that corresponds well with the Rokkoku Tectonic Line; this geological boundary is the likely cause of the dislocation of the seismogenic layer because it is intruded by serpentinite veins. A possible factor in the southern rupture termination of the 2016 Kumamoto Earthquake is the existence of a high-Vp/Vs body in the direction of southern rupture propagation. The provided details of this inhomogeneous barrier, which are inferred from the seismic velocity structures, may improve future seismic hazard assessments for a complex fault system composed of multiple segments.

Seismic tomographic interpretation of Paleozoic sedimentary sequences in the southeastern North Sea

Geophysics ◽  
2005 ◽  
Vol 70 (4) ◽  
pp. R45-R56 ◽  
Author(s):  
Lars Nielsen ◽  
Hans Thybo ◽  
Martin Glendrup
Keyword(s):  
North Sea ◽  
Velocity Structure ◽  
Seismic Velocity ◽  
P Wave ◽  
Wide Angle ◽  
North German Basin ◽  
Sedimentary Sequences ◽  
The North ◽  
Crystalline Crust ◽  
German Basin

Seismic wide-angle data were recorded to more than 300-km offset from powerful airgun sources during the MONA LISA experiments in 1993 and 1995 to determine the seismic-velocity structure of the crust and uppermost mantle along three lines in the southeastern North Sea with a total length of 850 km. We use the first arrivals observed out to an offset of 90 km to obtain high-resolution models of the velocity structure of the sedimentary layers and the upper part of the crystalline crust. Seismic tomographic traveltime inversion reveals 2–8-km-thick Paleozoic sedimentary sequences with P-wave velocities of 4.5–5.2 km/s. These sedimentary rocks are situated below a Mesozoic-Cenozoic sequence with variable thickness: ∼2–3 km on the basement highs, ∼2–4 km in the Horn Graben and the North German Basin, and ∼6–7 km in the Central Graben. The thicknesses of the Paleozoic sedimentary sequences are ∼3–5 km in the Central Graben, more than 4 km in the Horn Graben, up to ∼4 km on the basement highs, and up to 8 km in the North German Basin. The Paleozoic strata are clearly separated from the shallower and younger sequences with velocities of ∼1.8–3.8 km/s and the deeper crystalline crust with velocities of more than 5.8–6.0 km/s in the tomographic P-wave velocity model. Resolution tests show that the existence of the Paleozoic sediments is well constrained by the data. Hence, our wide-angle seismic models document the presence of Paleozoic sediments throughout the southeastern North Sea, both in the graben structures and in deep basins on the basement highs.

Seismic velocity structure and gravity anomalies: a comparison

1987 ◽  
Vol 140 (1) ◽  
pp. 115-120
Author(s):  
Yoshibumi Tomoda ◽  
Hiromi Fujimoto
Keyword(s):  
Velocity Structure ◽  
Seismic Velocity ◽  
Gravity Anomalies ◽  
Seismic Velocity Structure

What Is Fling Step? Its Theory, Simulation Method, and Applications to Strong Ground Motion near Surface Fault Ruptures

2021 ◽  
Author(s):  
Yoshiaki Hisada ◽  
Shinya Tanaka
Keyword(s):  
Velocity Structure ◽  
Seismic Velocity ◽  
Strong Motion ◽  
Theoretical Method ◽  
Simulation Method ◽  
Near Surface ◽  
Seismic Velocity Structure ◽  
Strong Motion Records ◽  
Near Fault ◽  
Fling Step

ABSTRACT We present the theory of the fling step and a theoretical method for simulating accurately the near-fault strong motions, and apply it to reproduce various strong-motion records near surface faults. Theoretically, the fling step is the contribution of the static Green’s function in the representation theorem (Hisada and Bielak, 2003), and we show that this theory holds for any seismic velocity structure. We first demonstrate the validity of this theory using theoretical solutions of a circular fault model in a homogeneous full-space. Next, we apply the theory to layered half-spaces, present a theoretical method based on the wavenumber integration method, and introduce various techniques to simulate the near-fault ground motions including fling steps with high accuracy. Finally, we demonstrate the effectiveness of the method by reproducing various strong-motion records near surface fault ruptures and discuss the characteristics of near-fault strong motions including the fling step and the forward directivity pulse. We made all of the software and data used in this article available on the internet.

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