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Titolo:
Normal mode composition of earthquake T phases
Autore:
DSpain, GL; Berger, LP; Kuperman, WA; Stevens, JL; Baker, GE;
Indirizzi:
Scripps Inst Oceanog, Marine Phys Lab, San Diego, CA 92152 USA Scripps Inst Oceanog San Diego CA USA 92152 Lab, San Diego, CA 92152 USA Maxwell Technol, San Diego, CA 92123 USA Maxwell Technol San Diego CA USA92123 l Technol, San Diego, CA 92123 USA
Titolo Testata:
PURE AND APPLIED GEOPHYSICS
fascicolo: 3, volume: 158, anno: 2001,
pagine: 475 - 512
SICI:
0033-4553(200102)158:3<475:NMCOET>2.0.ZU;2-F
Fonte:
ISI
Lingua:
ENG
Soggetto:
SOUND FIELD; WAVE-GUIDE; RANGE; OCEAN;
Keywords:
CTBT; IMS; T phase; hydroacoustic; normal modes;
Tipo documento:
Article
Natura:
Periodico
Settore Disciplinare:
Physical, Chemical & Earth Sciences
Citazioni:
47
Recensione:
Indirizzi per estratti:
Indirizzo: D'Spain, GL Scripps Inst Oceanog, Marine Phys Lab, San Diego, CA 92152 USAScripps Inst Oceanog San Diego CA USA 92152 ego, CA 92152 USA
Citazione:
G.L. D'Spain et al., "Normal mode composition of earthquake T phases", PUR A GEOPH, 158(3), 2001, pp. 475-512

Abstract

Understanding the nature of the coupling between the underwater acoustic field and the land seismic field is important for evaluating the performanceof the T-phase stations in the International Monitoring System for the Comprehensive Nuclear-Test-Ban Treaty. For upslope propagation in an ocean environment, the places where underwater acoustic field energy couples into the land seismic field are determined to first approximation by the local water depth and the normal mode composition of the acoustic energy. Therefore,the use of earthquake-generate T phases as natural probes of water-to-landcoupling characteristics is aided by knowledge of their modal composition. Data collected by a 200 element, 3000-m-aperture vertical hydrophone arrayduring a 1989 experiment in the deep northeast Pacific Ocean are used to determine the mode composition of T-phase arrivals from two mb 4.1 earthquakes near the west coast of the U.S., one occurring offshore and the other onland. Results from an eigenanalysis approach and conventional mode decomposition for the two events are consistent and show that at 5 Hz, the offshore event's arrivals have higher-order mode content compared to those from the event on land. Single hydrophone recordings at Pt. Sur of two m(b) 4.4 Hawaiian events in 1996 and 1997, one occurring offshore and the second on land, display time-frequency arrival structures that are explainable by the dispersion characteristics over the oceanic path. Although other effects dueto complex source time functions and shear wave and dispersive propagationeffects along the initial land path cannot be separated with these single element data, differences in these two events' arrival structures suggest differences in normal mode content consistent with those seen in the pair of1989 events. Ocean-path dispersion also appears to play a significant rolein determining the in-water arrival structure from a 1995 French nuclear test at Mururoa. Recordings of two Hawaiian events in 1997 by the T-phase station VIE and the seismic station at Berkeley illustrate that the water-land coupling confuses the relative timing between normal modes, resulting in apparent loss of information about the source.

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Documento generato il 26/09/20 alle ore 14:23:06