The possibility of inferring paleoseismicity from paleomagnetic dating of speleothems, western Japan   总被引：2，自引：0，他引：2  

Hayao Morinaga  Takafumi Yonezawa  Yasuhisa Adachi  Hiroo Inokuchi  Hiroya Goto  Katsumi Yaskawa 《Tectonophysics》1994,230(3-4):241-248

Paleomagnetic dating of continuously growing stalagmites by comparing their paleomagnetic records with a standard record, has been applied to study the paleoseismic history of a region of western Japan. Three stalagmites (speleothems), which are assumed to have started growing since collapse of the limestone blocks on which they are formed, were collected from two limestone caves located below the Akiyoshi plateau, western Japan. From the paleomagnetic results, it is estimated that they began to grow at 6000, 2500 and 2000 yr B.P., respectively. On the assumption that their growth began immediately after their host limestone blocks fell, these three ages are interpreted to indicate the dates of past earthquakes in this region which triggered the break-off and fall of the blocks. Earthquakes are suggested because many huge collapsed limestone blocks and speleothems are observed in many caves in this region.  相似文献   

The 1957 great Aleutian earthquake     

Jean M. Johnson  Yuichiro Tanioka  Larry J. Ruff  Kenji Satake  Hiroo Kanamori  Lynn R. Sykes 《Pure and Applied Geophysics》1994,142(1):3-28

The 9 March 1957 Aleutian earthquake has been estimated as the third largest earthquake this century and has the longest aftershock zone of any earthquake ever recorded—1200 km. However, due to a lack of high-quality seismic data, the actual source parameters for this earthquake have been poorly determined. We have examined all the available waveform data to determine the seismic moment, rupture area, and slip distribution. These data include body, surface and tsunami waves. Using body waves, we have estimated the duration of significant moment release as 4 min. From surface wave analysis, we have determined that significant moment release occurred only in the western half of the aftershock zone and that the best estimate for the seismic moment is 50–100×10²⁰ Nm. Using the tsunami waveforms, we estimated the source area of the 1957 tsunami by backward propagation. The tsunami source area is smaller than the aftershock zone and is about 850 km long. This does not include the Unalaska Island area in the eastern end of the aftershock zone, making this area a possible seismic gap and a possible site of a future large or great earthquake. We also inverted the tsunami waveforms for the slip distribution. Slip on the 1957 rupture zone was highest in the western half near the epicenter. Little slip occurred in the eastern half. The moment is estimated as 88×10²⁰ Nm, orM _w =8.6, making it the seventh largest earthquake during the period 1900 to 1993. We also compare the 1957 earthquake to the 1986 Andreanof Islands earthquake, which occurred within a segment of the 1957 rupture area. The 1986 earthquake represents a rerupturing of the major 1957 asperity.  相似文献   

Clockwise and anticlockwise rotation of Viti Levu, Fiji—in relation to the tectonic development of the North and the South Fiji Basin     

Hiroo Inokuchi  Katsumi Yaskawa  Peter Rodda 《Geophysical Journal International》1992,110(2):225-237

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A mechanical model for plate deformation associated with aseismic ridge subduction in the new hebrides arc   总被引：1，自引：0，他引：1  

Chung Wai-Ying  Hiroo Kanamori 《Tectonophysics》1978,50(1):29-40

Tectonic features associated with a subducting fracture zone-aseismic ridge system in the New Hebrides island arc are investigated. Several notable features including a discontinuity of the trench, peculiar locations of two major islands (Santo and Malekula), regional uplift, and the formation of a basin are interpreted as a result of the subduction of a buoyant ridge system. The islands of Santo and Malekula are probably formed from an uplifted mid-slope basement high while the interarc basin of this particular arc is probably a subsiding basin instead of a basin formed by backarc opening. The situation can be modeled by using a thin elastic half plate overlying a quarter fluid space with a vertical upward loading applied at the plate edge. This model is consistent with topographic and geophysical data. This study suggests that subduction of aseismic ridges can have significant effects on tectonic features at consuming plate boundaries.  相似文献   

Quantification of great earthquakes     

Hiroo Kanamori 《Tectonophysics》1978,49(3-4)

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Re-examination of the earth's free oxcillations excited by the Kamchatka earthquake of November 4, 1952     

Hiroo Kanamori 《Physics of the Earth and Planetary Interiors》1976,11(3):216-226

Benioff's suggestion that the 58-min period sinusoidal oscillation found on a Pasadena strain seismogram after the Kamchatka earthquake of November 4, 1952 may represent the earth's gravest normal mode is re-examined in terms of a slow large-scale post-seismic deformation. The mechanism and the seismic moment of the main shock of the Kamchatka earthquake are determined by using the amplitude and the initial phase of G₂ and R₂ recorded at Pasadena and R₆ recorded at Palisades. By constraining the dip angle and the strike of the fault at 30° (towards NW) and N34°E, respectively, on the basis of the geometry of the Benioff zone, the slip angle is determined as 110° which represents 74% thrust and 26% right-lateral faulting. The direction of the slip angle agrees with the slip direction of the Pacific plate. A seismic moment of 3.5 · 10²⁹ dyn cm is obtained. If a fault area of 650 · 200 km² is assumed, an average dislocation of 5 m is obtained. Spectral analyses of the Pasadena strain records show that the 58-min sinusoidal oscillation in fact consists of a spectral peak near 54 min which is very close to the ₀S₂ mode and other high-frequency peaks which can be correlated to the earth's normal modes. The records from two independent recording galvanometers correlate with each other very well, indicating that the recorded oscillation represents a real strain and not instrumental noise. The phase relation between the NS and EW components is consistent with the strain field associated with ₀S₂ mode. Although these results provide positive evidence for a slow post-seismic deformation, the cause of the abrupt termination of the oscillation and the excitation mechanism remain unresolved.  相似文献   

Source process and tectonic implications of the Spanish deep-focus earthquake of March 29, 1954     

Wai-Ying Chung  Hiroo Kanamori 《Physics of the Earth and Planetary Interiors》1976,13(2):85-96

The source process of the deep-focus Spanish earthquake of March 29, 1954 (m_b = 7.1, h = 630 km) has been studied by using seismograms recorded at teleseismic distances. Because of its unusual location, this earthquake is considered to be one of the most important earthquakes that merit detailed studies. Long-period body-wave records reveal that the earthquake is a complicated multiple event whose wave form is quite different from that of usual deep earthquakes. The total duration of P phases at teleseismic distances is as long as 40 s. This long duration may explain the considerable property damage in Granada and Malaga, Spain, which is rather rare for deep earthquakes. Using the azimuthal distribution of the differences between the arrival times of the first, the second and later P phases, the hypocenters of the later events are determined with respect to the first event. The focus of the second event is located on the vertical nodal plane of the first shock suggesting that this vertical plane is the fault plane. This fault plane which strikes in N2°E and dips 89.1°E defines a nearly vertical dip-slip fault, the block to the west moving downwards. The time interval and spatial separation between the first and the second events are 4.3 s and 19 km respectively, giving an apparent rupture velocity of 4.3 km/s which is about 74% of the S-wave velocity at the source. A third event occurred about 8.8 s after the first event and about 35.6 km from it. At least six to ten events can be identified during the whole sequence. The mechanism of some of the later events, however, seems to differ from the first two events. Synthetic seismograms are generated by superposition of a number of point sources and are matched with the observed signals to determine the seismic moment. The seismic moments of the later events are comparable to, or even larger than, that of the first. The total seismic moment is determined to be 7 · 10²⁷ dyn cm while the moments of the first and the second shocks are 2.1 · 10²⁶ dyn cm and 5.1 · 10²⁶ dyn cm, respectively. The earthquake may represent a series of fractures in a detached piece of the lithosphere which sank rapidly into the deep mantle preserving the heterogeneity of material property at shallow depths.  相似文献   

A slow earthquake     

Hiroo Kanamori  Gordon S. Stewart 《Physics of the Earth and Planetary Interiors》1979,18(3):167-175

Anomalous earthquakes such as creep events, tsunami earthquakes and silent earthquakes have been reported in the recent literature. In this paper we discuss an anomalous “slow earthquake” that occurred on June 6, 1960 in southern Chile. Although the surface-wave magnitude of this event is only 6.9, it excited anomalously large long-period multiple surface waves with a seismic moment of 5.6 · 10²⁷ dyn cm. The Benioff long-period seismogram of this earthquake recorded at Pasadena shows an extremely long, about 1.5–2 h coda of Rayleigh waves, with a period of 10–25 s. The coda length for other events with a comparable magnitude which occurred in the same region is about 10 min. This observation suggests that the long coda length is due to a long source rupture process which lasted at least 1 h. Although at least 15 distinct events can be identified in the coda, no short-period body waves were recorded corresponding to these, except for the first one. These results suggest that a relatively small (M_s ? 6.9) earthquake triggered a series of slow events; the duration of the whole sequence being longer than 1 h. This event probably occurred on a transform fault on the extension of the Chile Rise and provides important information regarding the nature of the transform fault.  相似文献   

The Montenegro,Yugoslavia, earthquake of April 15, 1979: source orientation and strength     

David M. Boore  John D. Sims  Hiroo Kanamori  Sam Harding 《Physics of the Earth and Planetary Interiors》1981,27(2):133-142

Long-period teleseismic P, S and Rayleigh waves and geologic considerations indicate that the Montenegro earthquake involved thrust faulting on a plane striking nearly parallel to the Adriatic coast and dipping ca. 15° toward the Yugoslav mainland. There is some support from modeling of body waves recorded on long-period WWSSN instruments for a focal depth of 22 km, but the possibility of a multiple source and the difficulty of matching some of the detailed characteristics of the P- and S-wave forms reduce our confidence in the determination of the depth. Fortunately, the source orientation and moment of the event are not sensitive functions of the depth. The long-period (256 s) moment was 4.6 × 10¹⁹ Nm (4.6 × 10²⁶ dyne-cm). The moment obtained by fitting the first cycle of P and S waves recorded on WWSSN long-period instruments is about four times smaller. This increase of moment with period is consistent with spectral estimates of the moment from SH waves recorded at SRO and ASRO stations.  相似文献   

Great earthquakes at island arcs and the lithosphere     

H. Kanamori 《Tectonophysics》1971

The occurrence of great earthquakes in the northwestern circum-Pacific belt is explained systematically in terms of the interaction between the oceanic and continental lithospheres. The great earthquakes in the Alaska-Aleutian region are considered to be a result of a rebound of the continental lithosphere which is dragged by the underthrusting oceanic lithosphere. The largest earthquakes in the Japan region are about one order of magnitude smaller than those in the Alaska-Aleutian region. This is interpreted as due to the weakening of the continental lithosphere caused by a frictional heating at the interface between the oceanic and the continental lithospheres. When the friction becomes very small because of the subsequent heating, a tensile force begins to prevail in the oceanic lithosphere. This tensile force is caused by a gravitational pull exerted by the sinking lithosphere. When this tensile stress surpasses the strength of the lithosphere, a large-scale normal fault occurs which extends through the entire thickness of the lithosphere. The intermittent slippages of the lithosphere on this fault plane are observed as great normal-fault earthquakes. The Sanriku earthquake of 1933 represents one of these earthquakes. The normal faulting accounts for the sharp bend of the lithosphere at the trench and the rapid increase of the dip angle of the deep seismic zone in going from northern Japan to the Izu-Bonin region. After repeated slippages, the sinking lithosphere becomes detached from the oceanic lithosphere and no further lithospheric interaction can take place. This picture is consistent with the complete lack of great shallow earthquakes in the Izu-Bonin region.  相似文献