Todorokite formation in seawater by microbial mediation     

Noburu Takematsu  Hiroo Kusakabe  Yoshio Sato  Shiro Okabe 《Journal of Oceanography》1988,44(5):235-243

Microbial manganese oxidation in seawater was carried out in enrichment cultures which were obtained from the seawater supply system at the Marine Science Museum, Tokai University (Shimizu-shi, Japan). The manganese oxide formed was well-crystallized todorokite. The major element composition was within the range of marine manganese concretions and the O/Mn molar ratio was 1.8. The conditions for formation of manganese oxide minerals in marine environments are discussed on the basis of these results.  相似文献   

Estimate of differential stress in the upper crust from variations in topography and strike along the San Andreas fault   总被引：3，自引：0，他引：3  

Yuri Fialko  Luis Rivera  Hiroo Kanamori 《Geophysical Journal International》2005,160(2):527-532

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A large normal-fault earthquake at the junction of the Tonga trench and the Louisville ridge     

Holly Eissler  Hiroo Kanamori 《Physics of the Earth and Planetary Interiors》1982,29(2):161-172

The source mechanism of a large (M_s ? 7.2) earthquake that occurred in the oceanic plate at the junction of the Tonga—Kermadec trench systems with the aseismic Louisville ridge is found by inverting long-period vertical-component Rayleigh waves recorded by the IDA network. The solution is an almost-pure normal fault, on a plane striking roughly parallel to the trench axis, with seismic moment of 1.7 × 10²⁷ dyn cm, and thus is among the ten largest documented shallow normal-fault earthquakes. A point-source depth of 20 km for the event is resolved by modeling teleseismic body waves; the actual rupture may have extended deeper, to 30 or 40 km. The earthquake was a multiple event, consisting of two sources separated by 16 s. A rupture velocity of 3.5 km s^?1 is inferred. The earthquake can be interpreted as tensional failure in the shallow portion of the downgoing plate caused by the gravitational pull of the slab. The Louisville ridge may be creating a local degree of decoupling of the oceanic plate from the overriding plate, and/or a zone of extension within the slab, which could enhance the effect of the gravitational forces in the shallower part of the downgoing plate. In particular, the earthquake could be associated with the break-up of the leading seamount of the ridge, which is currently right at the trench. Alternatively, the earthquake may have been caused by stresses associated with the bending of the plate prior to subduction.  相似文献   

Seismic coupling and uncoupling at subduction zones   总被引：1，自引：0，他引：1  

Larry Ruff  Hiroo Kanamori 《Tectonophysics》1983,99(2-4)

Seismic coupling has been used as a qualitative measure of the “interaction” between the two plates at subduction zones. Kanamori (1971) introduced seismic coupling after noting that the characteristic size of earthquakes varies systematically for the northern Pacific subduction zones. A quantitative global comparison of many subduction zones reveals a strong correlation of earthquake size with two other variables: age of the subducting lithosphere and convergence rate. The largest earthquakes occur in zones with young lithosphere and fast convergence rates, while zones with old lithosphere and slow rates are relatively aseismic for large earthquakes. Results from a study of the rupture process of three great earthquakes indicate that maximum earthquake size is directly related to the asperity distribution on the fault plane (asperities are strong regions that resist the motion between the two plates). The zones with the largest earthquakes have very large asperities, while the zones with smaller earthquakes have small scattered asperities. This observation can be translated into a simple model of seismic coupling, where the horizontal compressive stress between the two plates is proportional to the ratio of the summed asperity area to the total area of the contact surface. While the variation in asperity size is used to establish a connection between earthquake size and tectonic stress, it also implies that plate age and rate affect the asperity distribution. Plate age and rate can control asperity distribution directly by use of the horizontal compressive stress associated with the “preferred trajectory” (i.e. the vertical and horizontal velocities of subducting slabs are determined by the plate age and convergence velocity). Indirect influences are many, including oceanic plate topography and the amount of subducted sediments.All subduction zones are apparently uncoupled below a depth of about 40 km, and we propose that the basalt to eclogite phase change in the down-going oceanic crust may be largely responsible. This phase change should start at a depth of 30–35 km, and could at least partially uncouple the plates by superplastic deformation throughout the oceanic crust during the phase change.  相似文献   

Determination of earthquake early warning parameters, τ_c and P_d, for southern California     

Yih-Min Wu  Hiroo Kanamori  Richard M. Allen  Egill Hauksson 《Geophysical Journal International》2007,170(2):711-717

We explore a practical approach to earthquake early warning in southern California by determining a ground-motion period parameter  τ _c   and a high-pass filtered displacement amplitude parameter Pd from the initial 3 s of the P waveforms recorded at the Southern California Seismic Network stations for earthquakes with M > 4.0. At a given site, we estimate the magnitude of an event from  τ _c   and the peak ground-motion velocity ( PGV ) from Pd . The incoming three-component signals are recursively converted to ground acceleration, velocity and displacement. The displacements are recursively filtered with a one-way Butterworth high-pass filter with a cut-off frequency of 0.075 Hz, and a P -wave trigger is constantly monitored. When a trigger occurs,  τ _c   and Pd are computed. We found the relationship between  τ _c   and magnitude ( M ) for southern California, and between Pd and PGV for both southern California and Taiwan. These two relationships can be used to detect the occurrence of a major earthquake and provide onsite warning in the area around the station where onset of strong ground motion is expected within seconds after the arrival of the P wave. When the station density is high, the methods can be applied to multistation data to increase the robustness of onsite early warning and to add the regional warning approach. In an ideal situation, such warnings would be available within 10 s of the origin time of a large earthquake whose subsequent ground motion may last for tens of seconds.  相似文献   

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   

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