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Titolo:
Geodetic constraints on postseismic deformation following the 1990 M-s 7.8Luzon earthquake and implications for Luzon tectonics and Philippine Sea plate motion
Autore:
Beavan, J; Silcock, D; Hamburger, M; Ramos, E; Thibault, C; Feir, R;
Indirizzi:
Inst Geol & Nucl Sci, Lower Hutt, New Zealand Inst Geol & Nucl Sci Lower Hutt New Zealand ci, Lower Hutt, New Zealand Columbia Univ, Lamont Doherty Earth Observ, Palisades, NY 10964 USA Columbia Univ Palisades NY USA 10964 arth Observ, Palisades, NY 10964 USA Univ S Australia, Sch Geoinformat Planning & Bldg, Adelaide, SA 5001, Australia Univ S Australia Adelaide SA Australia 5001 Adelaide, SA 5001, Australia Indiana Univ, Dept Geol Sci, Bloomington, IN 47405 USA Indiana Univ Bloomington IN USA 47405 Geol Sci, Bloomington, IN 47405 USA Philippine Inst Volcanol & Seismol, Quezon City, Philippines Philippine Inst Volcanol & Seismol Quezon City Philippines Philippines Natl Mapping & Resource Informat Agcy, Manila, Philippines Natl Mapping & Resource Informat Agcy Manila Philippines a, Philippines
Titolo Testata:
GEOCHEMISTRY GEOPHYSICS GEOSYSTEMS
, volume: 2, anno: 2001,
pagine: NIL_1 - NIL_41
SICI:
1525-2027(20010926)2:<NIL_1:GCOPDF>2.0.ZU;2-F
Fonte:
ISI
Lingua:
ENG
Soggetto:
POSITIONING SYSTEM MEASUREMENTS; LEAST-SQUARES ALGORITHM; SAN-ANDREAS FAULT; CRUSTAL DEFORMATION; SOUTHERN CALIFORNIA; EASTERN INDONESIA; HALF-SPACE; CONVERGENCE; SLIP; GPS;
Keywords:
Luzon earthquake; Philippine fault; postseismic deformation; crustal rheology; Philippine plate motion;
Tipo documento:
Article
Natura:
Periodico
Settore Disciplinare:
Physical, Chemical & Earth Sciences
Citazioni:
77
Recensione:
Indirizzi per estratti:
Indirizzo: Beavan, J Inst Geol & Nucl Sci, POB 30-368, Lower Hutt, New Zealand Inst Geol & Nucl Sci POB 30-368 Lower Hutt New Zealand Zealand
Citazione:
J. Beavan et al., "Geodetic constraints on postseismic deformation following the 1990 M-s 7.8Luzon earthquake and implications for Luzon tectonics and Philippine Sea plate motion", GEOCH GEO G, 2, 2001, pp. NIL_1-NIL_41

Abstract

[1] We have obtained three epochs of high-quality dual-frequency GPS data at 15 stations in the Luzon, Philippines, region since the July 16, 1990, M-s 7.8 earthquake, from which we generate horizontal velocity fields at theEarth's surface for the 1993-1996 and 1996-1998 periods. We use these velocities, plus 1996-1998 GPS velocity results reported elsewhere from 13 additional stations, to show that present-day deformation in Luzon is dominatedby strike-slip motion along the Philippine fault system. The measured strike-slip rate across central Luzon is faster than the expected long-term slip rate on the fault, which we attribute to postseismic deformation following the 1990 earthquake. The 1993-1996 and 1996-1998 deformation patterns cannot be statistically distinguished within the similar to 10% uncertainties of the data. If the observed deformation is interpreted using an elastic half-space model with uniform slip below a subsurface locking depth, we find a fault slip rate of 40 mm/yr and a locking depth of similar to 15 km. Thisis too fast to be a steady interseismic rate, as it disagrees with what isknown from paleoseismic and other evidence about earthquake recurrence andlong-term slip rate on the Philippine fault system in central and northernLuzon. Also, a 15 km locking depth for steady interseismic slip is probably too shallow compared to the depth of rupture in the 1990 earthquake. If the deformation is instead interpreted with two types of viscoelastic model,we find that the observed velocities can be fit well for a range of valuesof lower lithosphere viscosity and long-term slip rate. Using a two dimensional (2-D) viscoelastic coupling model, the minimum allowable lower lithosphere viscosity is 0.5 x 10(19) Pa s, with an associated long-term slip rate of 15-22 mm/yr. Faster long-term slip rates also fit well, with correspondingly higher values of viscosity. With a possibly more realistic model that includes 3-D viscoelastic effects we find preferred long-term velocities in the range 20-35 mm/yr and viscosities in the range 2-6 x 10(19) Pa s. Our preferred viscosities correspond to Maxwell times on the order of 7-20% of the typical earthquake recurrence interval and are several times higher than values found for a number of Californian strike-slip earthquakes. Otherimplications of our 1993-1998 surface velocities are that the Philippine Sea-Eurasia (PH-EU) Euler vector of Seno et al. [1993] is a better description of the PH-EU convergence rate than a Euler vector recently estimated from GPS velocities in the northern PH and that the great majority of the normal component of PH-EU plate convergence is taking place west of Luzon, presumably largely at the Manila Trench. We also find that Luzon is rotating counterclockwise relative to PH at 1 degrees -2 degrees /Myr, only similar to25% of the rate recently suggested by other workers on the basis of limited GPS data.

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Documento generato il 22/01/20 alle ore 13:23:11