Anomalous high amplitude ratios of P5KP/PKPab and P4KP/P(S)cP observed globally around 1 Hz
Amplitude ratio of 30 short-period conspicuous P5KP and PKPab phases from five intermediate depth or deep events in Fiji-Tonga recorded at European stations around 150° distance shows a mean value two to three times the ratio of the synthetic amplitudes obtained by the normal-mode theory (and ak135...
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ftgfzpotsdam:oai:gfzpublic.gfz-potsdam.de:item_246906 2023-05-15T18:23:19+02:00 Anomalous high amplitude ratios of P5KP/PKPab and P4KP/P(S)cP observed globally around 1 Hz Ivan, M. Wang, R. 2013 application/pdf https://gfzpublic.gfz-potsdam.de/pubman/item/item_246906 https://gfzpublic.gfz-potsdam.de/pubman/item/item_246906_1/component/file_246905/20416.pdf eng eng info:eu-repo/semantics/altIdentifier/doi/10.1007/s10950-012-9330-7 https://gfzpublic.gfz-potsdam.de/pubman/item/item_246906 https://gfzpublic.gfz-potsdam.de/pubman/item/item_246906_1/component/file_246905/20416.pdf info:eu-repo/semantics/openAccess Journal of Seismology 550 - Earth sciences info:eu-repo/semantics/article 2013 ftgfzpotsdam https://doi.org/10.1007/s10950-012-9330-7 2022-09-14T05:54:04Z Amplitude ratio of 30 short-period conspicuous P5KP and PKPab phases from five intermediate depth or deep events in Fiji-Tonga recorded at European stations around 150° distance shows a mean value two to three times the ratio of the synthetic amplitudes obtained by the normal-mode theory (and ak135 model) or by full-wave theory (and PREM). There is a large variance in the results, also observed in five amplitude ratios from one event in Argentina observed at temporary stations in China around 156°. Global recordings of three major deep earthquakes in Fiji, Bonin, and Western Brazil observed at ASAR, WRA, and ZRNK arrays, at 59 North America stations and at six South Pole stations displayed conspicuous P4KP and PcP (or ScP) phases. The amplitude ratio values of P4KP vs P(S)cP are sometimes almost one order of magnitude larger than the corresponding values of the synthetics. In both cases, arrival times and slowness values (corrected for ellipticity and station elevation) at the distances up to 23° beyond the A cutoff point predicted by ray theory match both the synthetics, suggesting the observations are the AB branch of PmKP (m = 4, 5) around 1 Hz. In disagreement to ray theory, no reliable BC branch is observed neither on the recordings nor on the normal-mode synthetics. The high amplitude ratio values cannot be explained by realistic perturbations of the velocity or attenuation values of the global models in the proximity of the core-to-mantle boundary (CMB). We speculate that the focusing effects and/or strong scattering most likely associated to some anomalous velocity areas of the lowermost mantle are responsible for that. The results suggest limitations of the previous evaluations of the short-period attenuation in the outer core from PmKP amplitudes (m ≥ 3), irrespective of the fact that they are obtained by using ray theory, normal-mode or full-wave synthetics. Attempts to use PmKP arrival times in order to refine velocity structure in the proximity of CMB should be also regarded with care if the ... Article in Journal/Newspaper South pole GFZpublic (German Research Centre for Geosciences, Helmholtz-Zentrum Potsdam) Argentina South Pole Tonga ENVELOPE(7.990,7.990,63.065,63.065) Asar ENVELOPE(134.033,134.033,68.667,68.667) Journal of Seismology 17 2 453 464 |
institution |
Open Polar |
collection |
GFZpublic (German Research Centre for Geosciences, Helmholtz-Zentrum Potsdam) |
op_collection_id |
ftgfzpotsdam |
language |
English |
topic |
550 - Earth sciences |
spellingShingle |
550 - Earth sciences Ivan, M. Wang, R. Anomalous high amplitude ratios of P5KP/PKPab and P4KP/P(S)cP observed globally around 1 Hz |
topic_facet |
550 - Earth sciences |
description |
Amplitude ratio of 30 short-period conspicuous P5KP and PKPab phases from five intermediate depth or deep events in Fiji-Tonga recorded at European stations around 150° distance shows a mean value two to three times the ratio of the synthetic amplitudes obtained by the normal-mode theory (and ak135 model) or by full-wave theory (and PREM). There is a large variance in the results, also observed in five amplitude ratios from one event in Argentina observed at temporary stations in China around 156°. Global recordings of three major deep earthquakes in Fiji, Bonin, and Western Brazil observed at ASAR, WRA, and ZRNK arrays, at 59 North America stations and at six South Pole stations displayed conspicuous P4KP and PcP (or ScP) phases. The amplitude ratio values of P4KP vs P(S)cP are sometimes almost one order of magnitude larger than the corresponding values of the synthetics. In both cases, arrival times and slowness values (corrected for ellipticity and station elevation) at the distances up to 23° beyond the A cutoff point predicted by ray theory match both the synthetics, suggesting the observations are the AB branch of PmKP (m = 4, 5) around 1 Hz. In disagreement to ray theory, no reliable BC branch is observed neither on the recordings nor on the normal-mode synthetics. The high amplitude ratio values cannot be explained by realistic perturbations of the velocity or attenuation values of the global models in the proximity of the core-to-mantle boundary (CMB). We speculate that the focusing effects and/or strong scattering most likely associated to some anomalous velocity areas of the lowermost mantle are responsible for that. The results suggest limitations of the previous evaluations of the short-period attenuation in the outer core from PmKP amplitudes (m ≥ 3), irrespective of the fact that they are obtained by using ray theory, normal-mode or full-wave synthetics. Attempts to use PmKP arrival times in order to refine velocity structure in the proximity of CMB should be also regarded with care if the ... |
format |
Article in Journal/Newspaper |
author |
Ivan, M. Wang, R. |
author_facet |
Ivan, M. Wang, R. |
author_sort |
Ivan, M. |
title |
Anomalous high amplitude ratios of P5KP/PKPab and P4KP/P(S)cP observed globally around 1 Hz |
title_short |
Anomalous high amplitude ratios of P5KP/PKPab and P4KP/P(S)cP observed globally around 1 Hz |
title_full |
Anomalous high amplitude ratios of P5KP/PKPab and P4KP/P(S)cP observed globally around 1 Hz |
title_fullStr |
Anomalous high amplitude ratios of P5KP/PKPab and P4KP/P(S)cP observed globally around 1 Hz |
title_full_unstemmed |
Anomalous high amplitude ratios of P5KP/PKPab and P4KP/P(S)cP observed globally around 1 Hz |
title_sort |
anomalous high amplitude ratios of p5kp/pkpab and p4kp/p(s)cp observed globally around 1 hz |
publishDate |
2013 |
url |
https://gfzpublic.gfz-potsdam.de/pubman/item/item_246906 https://gfzpublic.gfz-potsdam.de/pubman/item/item_246906_1/component/file_246905/20416.pdf |
long_lat |
ENVELOPE(7.990,7.990,63.065,63.065) ENVELOPE(134.033,134.033,68.667,68.667) |
geographic |
Argentina South Pole Tonga Asar |
geographic_facet |
Argentina South Pole Tonga Asar |
genre |
South pole |
genre_facet |
South pole |
op_source |
Journal of Seismology |
op_relation |
info:eu-repo/semantics/altIdentifier/doi/10.1007/s10950-012-9330-7 https://gfzpublic.gfz-potsdam.de/pubman/item/item_246906 https://gfzpublic.gfz-potsdam.de/pubman/item/item_246906_1/component/file_246905/20416.pdf |
op_rights |
info:eu-repo/semantics/openAccess |
op_doi |
https://doi.org/10.1007/s10950-012-9330-7 |
container_title |
Journal of Seismology |
container_volume |
17 |
container_issue |
2 |
container_start_page |
453 |
op_container_end_page |
464 |
_version_ |
1766202884866703360 |