Spatial distribution of earthquakes in the Kii peninsula,Japan, south of the Median Tectonic Line     

Hiroo KanamoriKenshiro Tsumura 《Tectonophysics》1971

Precise data obtained by a high-sensitivity micro-earthquake observatory network are used to determine simultaneously the crustal structure and the spatial distribution of small earthquakes in the Kii peninsula region, Japan. The spatial distribution of hypocenters thus determined clearly shows two distinct groups of earthquakes: (1) a group of shallow (H ? 10 km) earthquakes on the western coast of the Kii peninsula near Wakayama; (2) a group of mantle earthquakes, having a depth ranging from 30 to 70 km and trending NE-SW, in the central part of the Kii peninsula. Along the trend of the second group, a marked structural anomaly is found which suggests the presence of a high-velocity zone at depths below 20 km. A projection of the hypocenters of the earthquakes belonging to the second group onto a vertical plane strikingNW-SE shows a wedge-like distribution to a depth of 70 km. The spatial relation between this wedge-like distribution and the 1944 Tonankai earthquake (M = 8.0) suggests a common tectonic process which is now taking place in the Kii peninsula region. The activity of the earthquakes of the first group terminates abruptly to the north at the Median Tectonic Line. This activity is represented by numerous but relatively small events (M < 5) without any conspicuous major earthquakes in history. It is suggested that the strength of the crust in this region of shallow activity is too weak to sustain stresses large enough to be released in a major event; rather, the stresses which probably originate from the tectonic activity represented by the earthquakes of the second group are released by numerous minor fracturings of the low-strength crust. A possibility of using the weak crust for detecting a remote stress accumulation is suggested.  相似文献   

Oxygen isotope fractionation factors between anhydrite and water from 100 to 550°C     

Hitoshi Chiba  Minoru Kusakabe  Shin-Ichi Hirano  Sadao Matsuo  Shigeyuki Somiya 《Earth and Planetary Science Letters》1981,53(1):55-62

Oxygen isotope exchange between anhydrite and water was studied from 100 to 550°C, using the partial equilibrium method. The exchange rate was extremely low in NaCl solution. In the lower-temperature range, acid solutions were used to produce sufficient reaction to determine the oxygen isotope fractionation factors. The fractionation factors obtained in the present study are definitely different from those given by Lloyd [8]. They are similar to those for the HSO₄^?-water system studied by Mizutani and Rafter [19], and are consistently 2‰ higher than those of the barite-water system by Kusakabe and Robinson [5]. The temperature dependence of the oxygen isotope fractionation factors was calculated by the least squares method in which the weight was taken to be inversely proportional to the experimental error. The fractionation is given by:10³lnαanhydrite-water=3.21×(10³/T)²?4.72Available δ¹⁸O values of natural anhydrite were used to test the validity of this expression. It is shown that this newly revised geothermometer can be successfully applied to natural hydrothermal anhydrite.  相似文献   

Crustal structure and temporal velocity change in southern California   总被引：3，自引：0，他引：3  

Hiroo Kanamori  David Hadley 《Pure and Applied Geophysics》1975,113(1):257-280

Summary About twenty blasts are used to determine crustal structure and to monitor temporal seismic velocity changes in southern California. The shot time is determined up to 10 msec by using a disposable pick-up placed directly on the explosive. About 17 permanent stations and 20 temporary stations are used for the recordings. With a fast paper speed (typically 1 cm/sec) and the WWVB radio signals superposed on the seismic trace, absolute timing accuracy of up to 10 msec is achieved. A representative structure thus determined consists of a 4 km thick 5.5 km/sec layer underlain successively by 23.4 km thick 6.3 km/sec layer, 5.0 km thick 6.8 km/sec layer and 7.8 km/sec half space. The details of the lower crust are somewhat uncertain. This structure can explain the travel time data, corrected for the station and source elevations and for the station delays, to ±0.15 sec. Small but systematic temporal velocity changes up to 3% have been found for some of the profiles. If the effect of the migration of the shot point is small enough, these changes are larger than experimental errors and represent real temporal change in the material property between the shot point and the stations.Contribution No. 2530, Division of Geological Sciences, California Institute of Technology, Pasadena, California.  相似文献   

Seismicity and the subduction process   总被引：1，自引：0，他引：1  

Larry Ruff  Hiroo Kanamori 《Physics of the Earth and Planetary Interiors》1980,23(3):240-252

There is considerable variation between subduction zones in the largest characteristic earthquake within each zone. Assuming that coupling between downgoing and upper plates is directly related to characteristic earthquake size, we have tested for correlations between variation in coupling and other physical features of subduction zones: the lateral extent and penetration depth of Benioff zones, age of subducting lithosphere, convergence rate, and back-arc spreading. Using linear multivariate regression, coupling is correlated with two variables: convergence rate and lithosphere age. Secondary correlations within the data set are penetration depth versus lithosphere age, and lateral extent versus convergence rate. An important additional correlation is that back-arc spreading is found to be associated with subduction zones where coupling is low (those characterised by small earthquakes). Taken together, the observed correlations suggest a simple qualitative model where convergence rate and lithosphere age determine the horizontal and sinking rates, respectively, of slabs: these parameters influence the seismic coupling in the subduction zone. In the limit of a fast sinking rate and slow convergence rate, back-arc spreading occurs and thereby appears to be a passive process.  相似文献   

Use of long-period surface waves for rapid determination of earthquake-source parameters   总被引：1，自引：0，他引：1  

Hiroo Kanamori  Jeffrey W. Given 《Physics of the Earth and Planetary Interiors》1981,27(1):8-31

A method for rapid retrieval of earthquake-source parameters from long-period surface waves is developed. With this method, the fault geometry and seismic moment can be determined immediately after the surface wave records have been retrieved. Hence, it may be utilized for warning of tsunamis in real time. The surface wave spectra are inverted to produce either a seismic moment tensor (linear) or a fault model (nonlinear). The method has been tested by using the IDA (International Deployment of Accelerographs) records. With these records the method works well for the events larger than M_s = 6, and is useful for investigating the nature of slow earthquakes.For events deeper than 30 km, all of the five moment tensor elements can be determined. For very shallow events (d ? 30 km) the inversion becomes ill-conditioned and two of the five source moment tensor elements become unresolvable. This difficulty is circumvented by a two-step inversion. In the first step, the unresolvable elements are constrained to be zero to yield a first approximation. In the second step, additional geological and geophysical data are incorporated to improve the first approximation. The effect of the source finiteness is also included.  相似文献   

Temporal changes in P-wave velocity in Southern California     

Hiroo Kanamori  Chung Wai-ying 《Tectonophysics》1974,23(1-2)

P-wave delays at Tinemaha, China Lake, Pasadena, Riverside, Hayfield and Barrett, stations of the CIT Southern California seismic network, are measured for three explosions in the Aleutians and six deep-focus earthquakes in the Marianas. Except at Riverside, no change in P-delays exceeding the experimental uncertainty, ± 0.2 sec, is found during the period from 1965 to 1971. At Riverside, however, P-delay in 1971 is at least 0.4 sec smaller than that in 1965, indicating a temporal P-velocity increase beneath Riverside from 1965 to 1971. Evidence supporting this result is obtained from the P-times at Riverside for quarry blasts at Corona (Δ ≈ 20 km). Precise travel-time measurements are made for eight blasts since 1949. The travel time changes as a function of time, ranging from 3.3 to 3.7 sec. This range of variation seems to be larger than the experimental uncertainty. The trend for the period from 1964 to 1969 is consistent with the temporal change in the teleseismic P-delays observed at Riverside. The observed change in P-delays is not related in any obvious way to past seismic activity; rather it might represent a large-scale fluctuation of the property of the crust caused possibly by change in the tectonic stress and fluid-vapor flow, and may be related to future earthquake activity.  相似文献   

Long-period ground motion in the epicentral area of major earthquakes     

Hiroo Kanamori 《Tectonophysics》1974,21(4):341-356

In view of the potential importance of long-period ground motion in the design of large structures, near-field ground displacement is computed by the elastic dislocation theory for several earthquake fault models. The validity of such computations is confirmed by comparing the computed seismogram with the observed long-period seismogram of the 1923 Kanto earthquake. The ground motions are computed for three hypothetical earthquakes, a hypothetical Kanto earthquake, Tokai earthquake and Nemuro-Oki earthquake. The location and the nature of the faulting of these earthquakes are predicted by plate tectonics and precise earthquake mechanism studies. Major conclusions are: Tokyo may suffer, in the hypothetical Kanto earthquake, ground motions about half as large as those experienced in the 1923 Kanto earthquake; Hamamatsu, a large city on the Tokai coast, may experience in the hypothetical Tokai earthquake ground motions which are as large as, or even larger than, those experienced in the epicentral area of the 1923 Kanto earthquake; the hypothetical Nemuro-Oki earthquake may cause ground motions as large as those experienced in the 1968 Tokachi-Oki earthquake on the coastal cities in Hokkaido.  相似文献   

Reply to comment by J. Trampert     

Jean-Paul Montagner  Phyllis Ho-Liu  Hiroo Kanamori 《Geophysical Journal International》1990,103(3):757-758

Books Reviewed in this Article:
Seismic tomography and mantle circulation Eds O'Nions, R. K. & Parsons, B., Royal Society of London Special Publication , 1989, ISBN 0854 033823.  相似文献   

An estimation of the electric potential field generated by the diurnal atmospheric tide with the first negative mode excited in the lower ionosphere     

Hiroo Murata 《Planetary and Space Science》1974,22(4):569-582

The electric potential field in the ionosphere, which is generated by the atmospheric tide with the diurnal first negative mode excited in the lower ionosphere, is estimated. An equivalent mode is used instead of the exact mode in the following approximations : (i) the horizontal structure of the energy input is composed of the first two terms of the series expansion of the Hough function with the associated Legendre functions, and (ii) the Coriolis force is assumed to be constant in the equation of motion and the value appropriate to colatitude 45 being used. It is found that the equivalent mode gives a good approximation of the exact mode at midlatitudes in the neutral atmosphere. The result shows that the oscillation with its temperature variation of about 40 K in the excitation region generates the horizontal electric potential field of 10^?3 V/m in magnitude. The horizontal pattern of the field distribution is similar to that estimated by many authors. The maximum vertical electric current is about 3 × 10^?9 A/m² in the dynamo layer. It is found that the “virtual current,” introduced by Volland (1970) as a vertical current in and above the dynamo layer, in order to obtain a better agreement between theory and observations of the location of the diurnal symmetric Sq current vortex, is actually to be expected. The vertical current is very small, but this small steady current is necessary for the electric potential field of the dynamo layer to be mapped into the magnetosphere along the lines of the geomagnetic field.  相似文献   

Regional S-wave structure for southern California from the analysis of teleseismic Rayleigh waves     

David Hadley  Hiroo Kanamori 《Geophysical Journal International》1979,58(3):655-666

Summary. Teleseismic Rayleigh waves, M_S > 7.0, in the period range 14 to 28 s, are well recorded by the short-period Benioff array within southern California. Multiple arrivals that hinder the determination of local phase velocity curves are detected by narrow band-pass filtering. The records are then windowed on distinct, coherent peaks that move uniformly across the array. Four to seven stations are included in the determination of both the phase velocity across the array and the incidence azimuth. For earthquakes in the western Pacific, the derived incidence azimuths are systematically rotated counterclockwise by 2–16°. Most of this rotation results from refraction at the continental shelf. Phase velocity data for both the southern Mojave—central Transverse Ranges and the Peninsular Ranges are inverted to obtain regional 5-wave velocity models. The starting models are constructed from travel-time studies of local sources, both natural and artificial. Poisson's ratio as a function of depth is calculated for these two regions. The comparison of Poisson's ratio with laboratory ultrasonic studies requires a quartz-rich crust within the southern Mojave—central Transverse Ranges and a mafic crust within the Peninsular Ranges.  相似文献