Precursory arrivals to PP

Kato, Mamoru; Hirahara, Kazuro

doi:10.1111/j.1365-246x.1991.tb06329.x

Cited by 4 publications

(3 citation statements)

References 13 publications

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“…PP and related energy have been used extensively for studying mantle structure (e.g. King et al 1975;Kato & Hirahara 1991;Revenaugh & Jordan 1991;Estabrook & Kind 1996;Weber & Wicks 1996;Flanagan & Shearer 1998;Rost & Weber 2002;Deuss et al 2006;Rost et al 2008). This source-receiver configuration and the selected seismic time window will allow the study of several subduction zones including Japan, Izu-Bonin and the Marianas (Fig.…”

Section: Datamentioning

confidence: 99%

Scattering beneath Western Pacific subduction zones: evidence for oceanic crust in the mid-mantle

Bentham

Rost

2014

Geophysical Journal International

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Small-scale heterogeneities in the mantle can give important insight into the dynamics and composition of the Earth's interior. Here, we analyse seismic energy found as precursors to PP, which is scattered off small-scale heterogeneities related to subduction zones in the upper and mid-mantle. We use data from shallow earthquakes (less than 100 km depth) in the epicentral distance range of 90 • -110 • and use array methods to study a 100 s window prior to the PP arrival. Our analysis focuses on energy arriving off the great circle path between source and receiver. We select coherent arrivals automatically, based on a semblance weighted beampower spectrum, maximizing the selection of weak amplitude arrivals. Assuming single P-to-P scattering and using the directivity information from array processing, we locate the scattering origin by ray tracing through a 1-D velocity model. Using data from the small-aperture Eielson Array (ILAR) in Alaska, we are able to image structure related to heterogeneities in western Pacific subduction zones. We find evidence for ∼300 small-scale heterogeneities in the region around the present-day Japan, Izu-Bonin, Mariana and West Philippine subduction zones. Most of the detected heterogeneities are located in the crust and upper mantle, but 6 per cent of scatterers are located deeper than 600 km. Scatterers in the transition zone correlate well with edges of fast features in tomographic images and subducted slab contours derived from slab seismicity. We locate deeper scatterers beneath the Izu-Bonin/Mariana subduction zones, which outline a steeply dipping pseudo-planar feature to 1480 km depth, and beneath the ancient (84-144 Ma) Indonesian subduction trench down to 1880 km depth. We image the remnants of subducted crustal material, likely the underside reflection of the subducted Moho. The presence of deep scatterers related to past and present subduction provides evidence that the subducted crust does descend into the lower mantle at least for these steeply dipping subduction zones. Applying the same technique to other source-receiver paths will increase our knowledge of the small-scale structure of the mantle and will provide further constraints on geodynamic models.

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Section: Datamentioning

confidence: 99%

Scattering beneath Western Pacific subduction zones: evidence for oceanic crust in the mid-mantle

Bentham

Rost

2014

Geophysical Journal International

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“…(1999)], investigations of upper‐mantle structure and discontinuities (e.g. Krishna & Kaila 1987; Kato & Hirahara 1991), studies of the core–mantle boundary and D″ layer (e.g. Rodgers & Wahr 1993; Obayashi & Fukao 1997; Sylvander et al .…”

Section: Introductionmentioning

confidence: 99%

“…van der Hilst et al (1997); Vasco & Johnson (1998); Bijwaard et al (1999)], investigations of upper-mantle structure and discontinuities (e.g. Krishna & Kaila 1987;Kato & Hirahara 1991), studies of the core^mantle boundary and D@ layer (e.g. Rodgers & Wahr 1993;Obayashi & Fukao 1997;Sylvander et al 1997), measurements of inner core anisotropy (Morelli et al 1986;Shearer et al 1988;Su & Dziewonski 1995) and inner core rotation (Su et al 1996).…”

Section: Introductionmentioning

confidence: 99%

Bias in reported seismic arrival times deduced from the ISC Bulletin

et al. 1999

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Summary The accurate timing of seismological data is crucial for most quantitative examinations in seismology. We present evidence that traveltime data from many stations contain systematic variations in timing which can be identified by checking the median of station delay times as a function of time. This function is expected to be constant but many deviations are found. Several hundred stations that report arrival times to the ISC have been examined. The median station delay times of almost 8 per cent of these stations show changes of more than 1 s and thus exceed the structural signal in the data. Temporal variations of 0.5–1 s are common. Changes in the distribution of observed earthquakes and other possible explanations of such variations have been tested and fail to explain most of the observations. Therefore, the bulk of the observed changes must be caused by flaws in the timing of the data or by biased picking of arrival times. For instance, at one station with a strong annual variation of noise level, the arrival times are on average picked several tenths of a second later during months with a high noise level. Because of their systematic nature, these errors will not necessarily cancel out by using the large number of traveltimes in the ISC Bulletin and may therefore introduce a bias in many investigations. If the observed timing variations are due to the recording equipment at the stations, the errors will be present in the digital waveform data as well. Tomographic studies could potentially be affected, but in particular studies of temporal variations of Earth structure based on traveltime data, e.g. inner core rotation, need to be looked at with caution as results might be influenced by station effects. The exact nature of the bias is study‐dependent and needs thorough investigation in each individual case.

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