Topography of the 660-km seismic discontinuity beneath Izu-Bonin: Implications for tectonic history and slab deformation

被引:52
作者
Castle, JC [1 ]
Creager, KC [1 ]
机构
[1] Univ Washington, Geophys Program, Seattle, WA 98195 USA
关键词
D O I
10.1029/98JB00503
中图分类号
P3 [地球物理学]; P59 [地球化学];
学科分类号
0708 ; 070902 ;
摘要
We analyze the P wave codas of 65 paths from deep northwestern Pacific earthquakes recorded by arrays of stations in Germany, the western United States, India, and Turkmenistan. We identify a phase resulting from a near-source S-to-P conversion at a nearly horizontal discontinuity ranging in depth from 650 to 730 km, which we interpret as a thermally depressed spinel to perovskite and magnesiowustite phase transition. We migrate these data along with 39 more from Wicks and Richards [1993], accounting for three-dimensional ray bending by the sloping discontinuity, to produce a high-resolution topography map of the 660-km discontinuity in the Izu-Bonin region. Assuming an equilibrium phase transition, we interpret the discontinuity depth in terms of local temperatures. The slab, if defined by a thermal anomaly greater than -400 degrees K, is only about 100 km thick near 28 degrees N suggesting the slab is penetrating into the lower mantle with little or no advective thickening. Farther to the north, however, cold material appears Spread out over a wide region, consistent with the slab having been laid down flat on the 660-km discontinuity as the trench retreated 2000 km eastward. Both the narrow slab to the south and the flat-lying slab to the north are consistent with recent high-resolution tomographic images. The depression to 745 km along the are is consistent with a maximum thermal anomaly of about 1100 degrees K. Along the entire are, the depression occurs directly beneath the deepest earthquakes, even where seismicity is dipping at 45 degrees and stops at 450 km depth, suggesting that the slab steepens to a vertical dip at the deepest seismicity. This change to a vertical orientation suggests that the slab loses strength temporarily through a physical process which causes the seismicity to increase dramatically and then abruptly cease.
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页码:12511 / 12527
页数:17
相关论文
共 59 条
[31]   SEISMICITY AND TECTONICS OF WESTERN PACIFIC - IZU-MARIANA-CAROLINE AND RYUKYU-TAIWAN REGIONS [J].
KATSUMATA, M ;
SYKES, LR .
JOURNAL OF GEOPHYSICAL RESEARCH, 1969, 74 (25) :5923-+
[32]   SEISMIC EVIDENCE FOR A 920-KM DISCONTINUITY IN THE MANTLE [J].
KAWAKATSU, H ;
NIU, FL .
NATURE, 1994, 371 (6495) :301-305
[33]   TRAVELTIMES FOR GLOBAL EARTHQUAKE LOCATION AND PHASE IDENTIFICATION [J].
KENNETT, BLN ;
ENGDAHL, ER .
GEOPHYSICAL JOURNAL INTERNATIONAL, 1991, 105 (02) :429-465
[34]   MANTLE PHASE-CHANGES AND DEEP-EARTHQUAKE FAULTING IN SUBDUCTING LITHOSPHERE [J].
KIRBY, SH ;
DURHAM, WB ;
STERN, LA .
SCIENCE, 1991, 252 (5003) :216-225
[35]   Metastable mantle phase transformations and deep earthquakes in subducting oceanic lithosphere [J].
Kirby, SH ;
Stein, S ;
Okal, EA ;
Rubie, DC .
REVIEWS OF GEOPHYSICS, 1996, 34 (02) :261-306
[36]   SEISMICITY, SHEAR FAILURE AND MODES OF DEFORMATION IN DEEP SUBDUCTION ZONES [J].
LUNDGREN, PR ;
GIARDINI, D .
PHYSICS OF THE EARTH AND PLANETARY INTERIORS, 1992, 74 (1-2) :63-74
[37]   N-TH ROOT PROCESS APPLIED TO SEISMIC ARRAY DATA [J].
MUIRHEAD, KJ ;
DATT, R .
GEOPHYSICAL JOURNAL OF THE ROYAL ASTRONOMICAL SOCIETY, 1976, 47 (01) :197-210
[38]   DIRECT EVIDENCE FOR THE UNDULATION OF THE 660-KM DISCONTINUITY BENEATH TONGA - COMPARISON OF JAPAN AND CALIFORNIA ARRAY DATA [J].
NIU, FL ;
KAWAKATSU, H .
GEOPHYSICAL RESEARCH LETTERS, 1995, 22 (05) :531-534
[39]   THE HORIZONTALLY LYING SLAB [J].
OKINO, K ;
ANDO, M ;
KANESHIMA, S ;
HIRAHARA, K .
GEOPHYSICAL RESEARCH LETTERS, 1989, 16 (09) :1059-1062
[40]   WESTWARD MIGRATION OF THE IZU-BONIN TRENCH, NORTHWARD MOTION OF THE PHILIPPINE SEA PLATE, AND THEIR RELATIONSHIPS TO THE CENOZOIC TECTONICS OF JAPANESE ISLAND ARCS [J].
OTSUKI, K .
TECTONOPHYSICS, 1990, 180 (2-4) :351-367