Whole mantle P wave tomography using P and PP‐P data

Abstract

1] We measured PP-P differential travel times on broadband seismograms of the Incorporated Research Institutions for Seismology (IRIS) network. The measurement was made by cross-correlating the observed PP waveform with the synthetic PP calculated from the observed P waveform. The effect of seawater reverberation on the measurement is taken into account if the PP bounce point is under ocean. The PP-P times measured after low-pass filtering is systematically shorter than those measured on raw broadband seismograms. We show that low-pass filtering tends to merge the precursory and postcursory phases into the main PP phase so that the measured PP-P times are artificially short. A cutoff frequency as high as 0.5 Hz is required to isolate the main PP. With such a high cutoff frequency, we obtained a total of about 7000 PP-P times. The residuals relative to a reference P velocity model are consistent with those calculated for the aspherical model WEPP2 [Obayashi et al., 1997] when the PP bounce points are located in the region well resolved by WEPP2. The PP-P times, combined with 2 million International Seismological Centre (ISC) first arrival times, were inverted for new model WEPP2 0 . This model renders a variance reduction of PP-P residuals of 63% without compromising the fit to P residuals used originally in WEPP2. In WEPP2 0 , the low velocity anomaly beneath Hawaii is limited in depth down to the uppermost part of the lower mantle. The high velocity anomaly of the Russian continental lithosphere is underlain in the mantle transition zone by a body of low velocity anomaly.INDEX TERMS: 7207 Seismology: Core and mantle; 7218 Seismology: Lithosphere and upper mantle; 8120 Tectonophysics: Dynamics of lithosphere and mantle-general; KEYWORDS: seismic tomography, plume structure, lithosphere structure Citation: Fukao, Y., A. To, and M. Obayashi, Whole mantle P wave tomography using P and PP-P data,

Deep Electromagnetic Studies from Land, Sea, and Space: Progress Status in the Past 10 Years

“…Fukao et al (2004) found that their cross-sections beneath Hawaii between 400 and 800 km depth was anomalously hot (with anomalies of order 200-300 K at a lateral scale of 1,000 km), a feature which is consistent with the results from both seismic and EM inversions. The lack of quantitative agreement between (Fukao et al 2003). High-and low-velocity anomalies are colored blue and red, respectively, in linear scale.…”

High‐velocity lid of East Antarctica: Evidence of a depleted continental lithosphere

“…High‐velocity anomalies extending to depths around 200 km are associated with the lithosphere of East Antarctica. Global P wave velocity tomography studies derived from travel times of P and PP waves have provided images beneath the region, but this resolution is poor because of the sparse station distribution and lack of seismicity in Antarctica [e.g., Fukao et al , 2003]. Global tomography derived from travel times of S waves has the same problem.…”

Origin of hotspots in the South Pacific: Recent advances in seismological and geochemical models

“…We used the travel times measured at PLUME and BBOBS stations together with the ISC P-wave arrival time data for global mantle raytheoretical tomography (e.g., Fukao et al, 2003). The spatial resolution achieved by our calculations in the lower mantle is estimated to be ~500 km.…”