Showing papers on "Hypocenter published in 1970"
TL;DR: In this paper, the authors measured the dip of downgoing lithospheric plates by inspecting published vertical sections of relocated hypocenters beneath Pacific and Indian island arcs and found that the maximum dip of the slab in a particular section, as determined by the hypocenter configuration, is inversely proportional to the distance from the section to the pole of relative motion of the two plates involved.
Abstract: Dips of downgoing lithospheric plates were measured by inspecting published vertical sections of relocated hypocenters beneath Pacific and Indian island arcs. For any one arc the maximum dip of the slab in a particular section, as determined by the hypocenter configuration, is inversely proportional to the distance from the section to the pole of relative motion of the two plates involved. Considering several oceanic arcs, a common inverse relationship exists between the dip and the relative rate of convergence of the plates at the location of the measurement. This dip-rate relationship may be a manifestation of the heavier downgoing plate that is sinking to an equilibrium (vertical) position.
93 citations
TL;DR: A small, dense network of independently recording portable seismograph stations was used to delineate the slip surface associated with the 1966 Parkfield-Cholame earthquake by precise three dimensional mapping of the hypocenters of its aftershocks.
68 citations
TL;DR: The largest earthquake to occur in the central Mississippi seismic region this century took place in south central Illinois on November 9, 1968 as mentioned in this paper, and the hypocenter and origin time based on observations from twelve regional stations varying in epicentral distance from 171 to 549 km, are 37.95°N, 88.48°W, h = 25 km, 0 = 17 h 01 m 42.2 s.
Abstract: The largest earthquake to occur in the central Mississippi seismic region this century took place in south central Illinois on November 9, 1968. The hypocenter and origin time based on observations from twelve regional stations varying in epicentral distance from 171 to 549 km, are 37.95°N, 88.48°W, h = 25 km, 0 = 17 h 01 m 42.0 s ± 0.2 s . Travel times of P at stations distant less than 2600 km indicate regional mantle variations, corresponding to rays bottoming at depths down to 650 km. Beyond this point travel times show a much smaller dependence, if any, on region. For stations in the central United States P times may be fitted by two straight line branches which intersect at about 600 km. The first branch corresponds to P n , the second to rays refracted from a surface at depth 97 km with a velocity below it of 8.37 km/sec. At larger distances (48°-100°) there are non-azimuth dependent residuals with respect to the Herrin Tables averaging about −1.5 sec, indicating a source-region correction with respect to these tables. Body wave magnitude was determined to be m b = 5.54 ± 0.44 for stations for which Δ > 25°, and m b = 5.44 ± 0.29, using Evernden9s formula, for P n in eastern North America. Surface waves give a value M s = 5.2. The fault plane solution determines two nodal planes each striking approximately north-south and dipping 45° to the east and to the west, respectively. This corresponds to dip slip, reverse motion, and to a horizontal east-west axis of compressional stress. While there are no mapped faults in the immediate epicentral region, the motion indicated is in conformity to that along the Wabash Valley Fault System 10 miles to the east.
64 citations
TL;DR: In an effort to monitor aftershock activity following the southern Illinois earthquake of November 9, 1968, a network of ten high gain seismic stations was established in the vicinity of the epicenter of the earthquake as discussed by the authors.
Abstract: In an effort to monitor aftershock activity following the southern Illinois earthquake of November 9, 1968, a network of ten high gain seismic stations was established in the vicinity of the epicenter of the earthquake. The network began recording on the fourth day after the earthquake and operated for a period of ten days. During this time only one very small aftershock was recorded. The hypocenter of this shock was about 10 km south and at the same depth as that of the main shock. Permanent stations of the region recorded two other aftershocks within two days of the main shock, and one more three and a half months later. The exceptionally low level of aftershock activity is an anomalous feature of the Southern Illinois-Southeast Missouri seismic zone.
12 citations
10 Jun 1970
TL;DR: In this article, the authors used old seismological data to re-evaluate the Great Kanto Earthquake of September 1, 1923 and determined the hypocenter parameters as: origin time, 2h58m32s; latitude 35.4°N; longitude, 139.2°E; depth, 0 to 10km.
Abstract: Old seismological data were used to re-evaluate the Great Kanto Earthquake of September 1, 1923. On the basis of reported P times at about one hundred stations the hypocenter parameters were determined as: origin time, 2h58m32s; latitude 35.4°N; longitude, 139.2°E; depth, 0 to 10km. The above epicenter may be uncertain by ±15 km. The surface-wave magnitude was re-evaluated using seismograms from 17 stations. The average value of 8.16 was obtained.
9 citations