Abstract. It has been proposed that intermediate-and deep-focus earthquakes occur on preexisting planes of weakness that were created at shallow depth. The purpose of this study is to test this hypothesis. We examined fault plane solutions for 360 events that occurred in the Tonga subduction zone from January 1976 to February 1999. For events in the slab, each fault plane solution is rotated by the slab dip angle so that the slab is in its original horizontal position. We then compare fault plane solutions for events in the slab with those for events at the outer rise. We find that an asymmetric fault system, corresponding to that found for outer rise events, persists down to about 450 km depth. This suggests that earthquakes down to this depth are caused by the reactivation of preexisting faults created in the oceanic plate before subduction. A similar pattern, though less well constrained, is found in the Kurile subduction zone down to 200 km depth. For earthquakes deeper than 450 km the fault plane solutions are much more scattered. In some places the fault plane pattern suggests the creation of new fault planes along orientations of maximum shear with zero internal friction. The pattern of fault plane solutions in particular localized volumes cannot be easily explained by the creation of new faults in the direction of maximum shear under a coherent regional tectonic stress field. Thus, either a highly heterogeneous stress field exists or preexisting planes of weakness also account for some deep earthquakes.
Cu/Cu2O/Cu/TiO2 catalyst was fabricated by in-situ photoreduction from Cu2O/TiO2, and it showed an excellent photocatalytic performance and high stability for H2 evolution. The interlayer metallic Cu provided a bridge for electrons fast transfer from TiO2 to Cu2O.
The 1994 Bolivian Earthquake (Mw=8.3) was recorded on‐scale by 8 very‐broadband stations deployed approximately 600 km south of the epicenter. When these seismograms are carefully converted to ground displacement, there appears to be a static offset which is on order of 2 cm. We have modeled the waveforms with a synthetic waveform method that contains near‐, intermediate‐ and far‐field terms. Although the synthetics are only calculated for an elastic half‐space, they compare favorably with the observed waveform in terms of shape. However, the theoretical amplitude is 1/2 of the observed static offset, which probably reflects the limitations of a homogeneous half‐space model and/or the instabilities in deconvolution.
21 earthquakes recorded by a temporary seismic network in the Changbaishan Tianchi volcanic area in Northeast China operated during the summer of 2002 and 2003 were analyzed to estimate the S coda attenuation. The attenuation quality factor Q c was estimated using the single scattering attenuation model of Sato (1977) in the frequency band from 4 to 24 Hz. All the events studied in this paper occurred at depths from 2 to 6 km with ML of 1.4-2.8. The epicentral distances are less than 25 km. For all events which occurred near the Tianchi Lake (caldera), the Q c patterns obtained at the stations near the lake are similar, and the Q c values are relatively small. At the stations located about 15 km east of the Tianchi Lake, however, the average Q c is significantly higher. For an event which occurred 25km from the lake to the west, Q c patterns derived at the stations near the lake are quite similar to the above mentioned Q c for stations located in the east. Further study shows that Q c value in the north and central areas of the volcano is relatively lower than that in the surrounding area. Compared to other volcanic areas in the world, the average Q c of the Changbaishan Tianchi volcanic area is obviously lower. The deep seismic sounding and teleseismic receiver function studies indicated more than one lower velocity layer in the crust. The MT studies suggested the presence of high conductive bodies beneath the area. We interpret the strong attenuation of coda waves near the Changbaishan Tianchi volcano as being possibly related to high temperature medium caused by shallow magma chambers.
Abstract. The Paleogene sedimentary records from southern China hold important clues to the impacts of the Cenozoic climate changes on low-latitudes. However, although there are extensive Paleogene terrestrial archives and some contain abundant fossils in this region, few are accurately dated and have a temporal resolution adequate to decipher climate changes. Here we present a detailed stratigraphic and paleomagnetic study of a fossiliferous late Paleogene succession in the Maoming Basin, Guangdong Province. The succession consists of oil shale of the Youganwo Formation (Fm) in the lower part and massive pebbly coarse sandstones of the overlying Huangniuling Fm in the upper part. The conformable transition from oil shale to sandstones represents a major depositional environmental change from a lacustrine to a deltaic environment. The substantially refined chronostratigraphic framework is established based on the litho-, bio-, cyclo-, and magnetostratiphic data that place the environmental transition at 33.88 Ma, coinciding with the Eocene–Oligocene climate transition (EOT) at ~ 33.7 to ~ 33.9 Ma. We suggest that the transition from a lacustrine to deltaic environment in Maoming Basin represents terrestrial responses to the EOT and indicates a significant reduction in hydrodynamics in low-latitude regions during the global cooling at EOT.
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