The Characteristics of J-Array Seismograms.

Morita, Yoshinori

doi:10.4294/jpe1952.44.657

Cited by 32 publications

(7 citation statements)

References 18 publications

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“…Nonetheless, waveforms can be obtained from one central data center. An attempt to unify the J‐array has been started by building the “New‐J‐Array” [ Morita , 1996].…”

Section: Arraysmentioning

confidence: 99%

Array Seismology: Methods and Applications

Rost

Thomas

2002

Reviews of Geophysics

836

637

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Since their development in the 1960s, seismic arrays have given a new impulse to seismology. Recordings from many uniform seismometers in a well‐defined, closely spaced configuration produce high‐quality and homogeneous data sets, which can be used to study the Earth's structure in great detail. Apart from an improvement of the signal‐to‐noise ratio due to the simple summation of the individual array recordings, seismological arrays can be used in many different ways to study the fine‐scale structure of the Earth's interior. They have helped to study such different structures as the interior of volcanos, continental crust and lithosphere, global variations of seismic velocities in the mantle, the core‐mantle boundary and the structure of the inner core. For this purpose many different, specialized array techniques have been developed and applied to an increasing number of high‐quality array data sets. Most array methods use the ability of seismic arrays to measure the vector velocity of an incident wave front, i.e., slowness and back azimuth. This information can be used to distinguish between different seismic phases, separate waves from different seismic events and improve the signal‐to‐noise ratio by stacking with respect to the varying slowness of different phases. The vector velocity information of scattered or reflected phases can be used to determine the region of the Earth from whence the seismic energy comes and with what structures it interacted. Therefore seismic arrays are perfectly suited to study the small‐scale structure and variations of the material properties of the Earth. In this review we will give an introduction to various array techniques which have been developed since the 1960s. For each of these array techniques we give the basic mathematical equations and show examples of applications. The advantages and disadvantages and the appropriate applications and restrictions of the techniques will also be discussed. The main methods discussed are the beam‐forming method, which forms the basis for several other methods, different slant stacking techniques, and frequency–wave number analysis. Finally, some methods used in exploration geophysics that have been adopted for global seismology are introduced. This is followed by a description of temporary and permanent arrays installed in the past, as well as existing arrays and seismic networks. We highlight their purposes and discuss briefly the advantages and disadvantages of different array configurations.

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“…Nonetheless, waveforms can be obtained from one central data center. An attempt to unify the J‐array has been started by building the “New‐J‐Array” [ Morita , 1996].…”

Section: Arraysmentioning

confidence: 99%

Array Seismology: Methods and Applications

Rost

Thomas

2002

Reviews of Geophysics

836

637

View full text Add to dashboard Cite

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“…We use 28,732 waveforms from 586 teleseismic events whose epicentral distances are 30–90°, and magnitudes are greater than 5.5. The waveform data were obtained from 78 stations of Hi‐net established by the National Research Institute for Earth Science and Disaster Prevention (NIED) [ Obara et al , 2005], and from 61 stations of the J‐array established by the Japan Meteorological Agency (JMA), Kyushu University, Kagoshima University and Kyoto University [ Morita , 1996] (Figure 1). We use waveform data from Hi‐net and the J‐array, recorded from June 2001 to May 2010 and from August 1996 to October 2009, respectively.…”

Section: Discussionmentioning

confidence: 99%

Water transportation through the Philippine Sea slab subducting beneath the central Kyushu region, Japan, as derived from receiver function analyses

Abe¹,

Ohkura²,

Hirahara³

et al. 2011

Geophys. Res. Lett.

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Receiver function analyses are performed to detect seismic velocity discontinuities in the uppermost mantle beneath the Kyushu subduction zone, Japan. The Philippine Sea slab subducting beneath Kyushu is young (26–50 Ma) and steeply dipping (at greater than 30°). We detect a seismic velocity contrast larger than 10% corresponding to the oceanic Moho down to 90 km in depth, implying that the subducting oceanic crust contains more than 3.0 wt.% water down to this depth. We also detect a discontinuity with downward decreasing seismic velocity at depths of 50–80 km, which is parallel to the oceanic Moho and 10 km shallower than it. This fact indicates that there is a sharp discontinuity between the mantle wedge and the hydrous oceanic crust. The existence of such a sharp discontinuity would require a large temperature gradient around the boundary or a permeability barrier at the upper boundary of the slab. We delineate the continental Moho with downward decreasing seismic velocity and the upper boundary of the slab with upward decreasing seismic velocity beneath the forearc region, which implies the existence of serpentinite and/or free fluid which causes high pore pressure in the forearc mantle.

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“…Figure 1 shows the waveforms of an event that occurred near Santiago, Chile, on June 24,1991 (depth = 558 km, m b = 6.4).We can identify both common phases, such as the DF and AB branches of PKBPPand PPPand uncommon phases, such as PcPPKPScPPKPand ScSPKP Some phases,such as those labeled XI to X5, have not yet been identified. Morita [1996] sug gested that the X3 and X4 phases might be PcP 66 0 PKP and PcP 4] Q PKPrespectively. It is very important to study such new and unknown phases since they provide possibili ties of obtaining new knowledge about the structures of Earth's interior.…”

Section: "°3mentioning

confidence: 99%

J‐Array Project seismic data now on CD‐ROM

1999

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Two CD‐ROMs containing seismic waveform data obtained from the J‐array Project are now available.The J‐array was a large‐aperture seismic array extending over all of Japan. It consisted of 14 regional seismic networks and more than 200 stations. The project was concerned with detecting small‐amplitude waves that are refracted, reflected, converted, or scattered from seismic velocity discontinuities existing deep within the Earth, and with studying the detailed structure and regional variations of the core, lower mantle, and upper mantle. Continuous digital seismic waveform data were recorded at the rate of 20 Hz with short period seismometers developed under Japan's national program for earthquake prediction. The J‐array project began in April 1991 and continued for 3 years at most of the networks. Many studies have been done with the data, including investigations of the structure of the upper mantle, lower mantle discontinuities, D″ layer, and core. Anyone interested in using the data can refer to J‐array Group [1993] for more information.

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The Characteristics of J-Array Seismograms.

Cited by 32 publications

References 18 publications

Array Seismology: Methods and Applications

Array Seismology: Methods and Applications

Water transportation through the Philippine Sea slab subducting beneath the central Kyushu region, Japan, as derived from receiver function analyses

J‐Array Project seismic data now on CD‐ROM

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