Frequency-dependent attenuation of shear waves in the crust of the southern Kanto area, Japan

1994 ◽  
Vol 84 (5) ◽  
pp. 1387-1396
Author(s):  
Shigeo Kinoshita
Keyword(s):  
Shear Waves ◽  
Strong Motion ◽  
Body Waves ◽  
Philippine Sea Plate ◽  
Eurasian Plate ◽  
Philippine Sea ◽  
Motion Data ◽  
Basement Rocks ◽  
Acceleration Data ◽  
Attenuation Characteristics

Abstract The attenuation characteristics of shear waves in the crust of the southern Kanto area, central Japan, were estimated using strong-motion data, including acceleration data recorded in the pre-Tertiary basement rocks by means of downhole observation. The quality factor Qs(f) was determined for a range of discrete frequencies from 0.5 to 16 Hz from the analysis of data from 13 local earthquakes with focal depths of less than about 50 km that occurred in the Philippine Sea plate and in the boundary zone between the lower part of the Eurasian plate and the upper part of the Philippine Sea plate. The estimated 1/Qs(f) shows a peaked structure in this frequency range on the assumption that the geometrical spreading exponent is -1 (body waves). The estimated peak 1/Qs(f) is of the order of 10-2 at 0.8 Hz.

scholarly journals Large-scale slope failure and active erosion occurring in the southwest Ryukyu fore-arc area

2001 ◽  
Vol 1 (4) ◽  
pp. 203-211 ◽  
Author(s):  
T. Matsumoto ◽  
M. Kimura ◽  
M. Nakamura ◽  
T. Ono
Keyword(s):  
Large Scale ◽  
Slope Failure ◽  
Gravitational Instability ◽  
Plate Boundary ◽  
Philippine Sea Plate ◽  
Eurasian Plate ◽  
Philippine Sea ◽  
Topographic Features ◽  
Ishigaki Island ◽  
Tensional Stress

Abstract. The southwestern Ryukyu area east of Taiwan Island is an arcuate boundary between Philippine Sea Plate and Eurasian Plate. The topographic features in the area are characterised by (1) a large-scale amphitheatre off Ishigaki Island, just on the estimated epicentre of the tsunamigenic earthquake in 1771, (2) lots of deep sea canyons located north of the amphitheatre, (3) 15–20 km wide fore-arc basin, (4) 15–20 km wide flat plane in the axial area of the trench, (5) E-W trending half grabens located on the fore-arc area, etc., which were revealed by several recent topographic survey expeditions. The diving survey by SHINKAI6500 in the fore-arc area on a spur located 120 km south of Ishigaki Island was carried out in 1992. The site is characterised dominantly by rough topography consisting of a series of steep slopes and escarpments. A part of the surface is eroded due to the weight of the sediment itself and consequently the basement layer is exposed. The site was covered with suspended particles during the diving, due to the present surface sliding and erosion. The same site was resurveyed in 1997 by ROV KAIKO, which confirmed the continuous slope failure taking place in the site. Another example that was observed by KAIKO expedition in 1997 is a largescale mud block on the southward dipping slope 80 km south of Ishigaki Island. This is apparently derived from the shallower part of the steep slope on the southern edge of the fan deposit south of Ishigaki Island. The topographic features suggest N-S or NE-SW tensional stress over the whole study area. In this sense, the relative motion between the two plates in this area is oblique to the plate boundary. So, the seaward migration of the plate boundary may occur due to the gravitational instability at the boundary of the two different lithospheric structures. This is evidenced by a lack of accretionary sediment on the fore-arc and the mechanism of a recent earthquake which occurred on 3 May 1998 in the Philippine Sea Plate 250 km SSE of Ishigaki Island.

scholarly journals Upper-mantle density structure in the Philippine Sea and adjacent region and its relation to tectonics

2019 ◽  
Vol 219 (2) ◽  
pp. 945-957
Author(s):  
Qing Liang ◽  
Chao Chen ◽  
Mikhail K Kaban ◽  
Maik Thomas
Keyword(s):  
Upper Mantle ◽  
Conversion Factor ◽  
High Density ◽  
Philippine Sea Plate ◽  
Gravity Inversion ◽  
Depth Range ◽  
Density Structure ◽  
Adjacent Region ◽  
Eurasian Plate ◽  
Philippine Sea

SUMMARY The evolution of the Philippine Sea Plate (PSP) since Jurassic is one of the key issues in the dynamics of lithosphere and mantle. The related studies benefited mostly from seismic tomography which provides velocity structures in the upper mantle. However, the upper-mantle structure is not well resolved compared to the continental areas due to the lack of seismic data in the Philippine Sea. We employ a 3-D gravity inversion constrained by an initial model based on the S-wave tomography (SL2013sv; Schaeffer & Lebedev 2013) to image the density structure of the upper mantle of the PSP and adjacent region. The resulting model shows a three-layer pattern of vertical high-low-high density variation in the upper mantle under the PSP. The thin high-density layer evidences for strong oceanic lithosphere in the West Philippine Sea. The relatively low dense mantle located below the PSP possibly originates from the asthenosphere. The PSP differs from the Pacific and the Indian-Australian plates in the whole depth range, while its structure is similar to the eastern Eurasian and Sunda plates. In the depth range, 200–300 km, the relative high-density zone beneath PSP extends to the Sunda Plate and to the eastern Eurasian Plate. We further estimated the conversion factor of our density model and the velocity model (SL2013sv; Schaeffer & Lebedev 2013) in order to locate the changes of compositional effects in the upper mantle. The negative conversion factor indicates that the compositional changes primarily affect the density anomalies beneath the PSP. We, therefore, describe the layered density structures as ‘sandwich’ pattern, which is unique and different from adjacent regions.

Detailed Attenuation Study of Shear Waves in the Kumaon Himalaya, India, Using the Inversion of Strong‐Motion Data

2015 ◽  
Vol 105 (4) ◽  
pp. 1836-1851 ◽  
Author(s):  
Parveen Kumar ◽  
A. Joshi ◽  
Sandeep ◽  
Ashvini Kumar ◽  
R. K. Chadha
Keyword(s):  
Shear Waves ◽  
Strong Motion ◽  
Strong Motion Data ◽  
Motion Data ◽  
Kumaon Himalaya

Processed strong-motion data for the El Salvador earthquake of June 19, 1982

1988 ◽  
Author(s):  
Kenneth W. Campbell ◽  
Sylvester Theodore Algermissen
Keyword(s):  
El Salvador ◽  
Strong Motion ◽  
Strong Motion Data ◽  
Motion Data

scholarly journals Configuration and structure of the Philippine Sea Plate off Boso, Japan: constraints on the shallow subduction kinematics, seismicity, and slow slip events

2019 ◽  
Vol 71 (1) ◽  
Author(s):  
Aki Ito ◽  
Takashi Tonegawa ◽  
Naoki Uchida ◽  
Yojiro Yamamoto ◽  
Daisuke Suetsugu ◽  
...  
Keyword(s):  
Receiver Function ◽  
Function Analysis ◽  
Philippine Sea Plate ◽  
Slow Slip ◽  
Low Velocity ◽  
Slow Slip Events ◽  
Philippine Sea ◽  
Receiver Function Analysis ◽  
Eastern Edge ◽  
Upper Boundary

Abstract We applied tomographic inversion and receiver function analysis to seismic data from ocean-bottom seismometers and land-based stations to understand the structure and its relationship with slow slip events off Boso, Japan. First, we delineated the upper boundary of the Philippine Sea Plate based on both the velocity structure and the locations of the low-angle thrust-faulting earthquakes. The upper boundary of the Philippine Sea Plate is distorted upward by a few kilometers between 140.5 and 141.0°E. We also determined the eastern edge of the Philippine Sea Plate based on the delineated upper boundary and the results of the receiver function analysis. The eastern edge has a northwest–southeast trend between the triple junction and 141.6°E, which changes to a north–south trend north of 34.7°N. The change in the subduction direction at 1–3 Ma might have resulted in the inflection of the eastern edge of the subducted Philippine Sea Plate. Second, we compared the subduction zone structure and hypocenter locations and the area of the Boso slow slip events. Most of the low-angle thrust-faulting earthquakes identified in this study occurred outside the areas of recurrent Boso slow slip events, which indicates that the slow slip area and regular low-angle thrust earthquakes are spatially separated in the offshore area. In addition, the slow slip areas are located only at the contact zone between the crustal parts of the North American Plate and the subducting Philippine Sea Plate. The localization of the slow slip events in the crust–crust contact zone off Boso is examined for the first time in this study. Finally, we detected a relatively low-velocity region in the mantle of the Philippine Sea Plate. The low-velocity mantle can be interpreted as serpentinized peridotite, which is also found in the Philippine Sea Plate prior to subduction. The serpentinized peridotite zone remains after the subduction of the Philippine Sea Plate and is likely distributed over a wide area along the subducted slab.

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