ISSN:0094-8276    

DOI:10.1029/GL013i003p00167

年代:1986

数据来源: WILEY

摘要:

Operators of a deep ocean hydrophone array near Wake Island in the northwest Pacific Basin have located several previously unreported earthquakes within 20° of Wake Island in the "aseismic" interior of the Pacific plate, and have suggested high attenuation in the source region to explain why these events have not been reported by seismological agencies. The largest such earthquake occurred on 1983 June 29, in the Kiribati region; readings were submitted to the International Seismological Centre, but the earthquake was excluded from the final analysis because of doubt about its location and interfering arrivals from other earthquakes. Closer examination now provides a well‐determined seismological location and a magnitude of 4.7 (mb). Neither amplitudes nor frequency content of Australian records of the Kiribati earthquake support the existence of a region of abnormally high attenuation beneath the source. We suggest that the higher magnitudes reported from the hydrophone measurements result from the efficient coupling of energy from shallow intraplate earthquakes in the Pacific Basin into the Po/Sowavegui

ISSN:0094-8276    

DOI:10.1029/GL013i003p00169

年代:1986

数据来源: WILEY

摘要:

Observations of three‐dimensional ground motion at a single point on the surface of the Earth following an earthquake can be sufficient to determine the zeroth order moment tensor of the event. We adapt the centroid‐moment tensor (CMT) method [Dziewonski et al., 1981] of analysis to single station data and apply it to the September 19, 1985 Michoacan earthquake. The obtained mechanism indicates faulting on a shallow plane, consistent with the ongoing subduction of the Cocos plate. The scalar moment is 1.3 × 1028dyne‐cm. A direct deconvolution of the observed P‐wave train indicates that the moment release occurred in two subevents, each of 20 seconds duration with a peak‐to‐peak separation in time o

ISSN:0094-8276    

DOI:10.1029/GL013i003p00173

年代:1986

数据来源: WILEY

摘要:

Earthquake focal mechanisms for a selected group of crustal earthquakes located in Alaska and neighboring areas have been compiled from various sources and regional characteristics of the horizontal stress have been deduced for the region from the mechanism solutions. The results show that the compressional stress regime of southern coastal areas continues inland through central Alaska and extends in a northeast direction. The western part of Alaska, including Chukotka and the Bering Sea adjoining Alaska and the Aleutian Island chain constitute a tensional stress regime.

ISSN:0094-8276    

DOI:10.1029/GL013i003p00177

年代:1986

数据来源: WILEY

摘要:

A melting experiment has been made on a natural lherzolite (spinel lherzolite, KLB‐1) at 20 GPa and 2160°C under hydrous conditions. The stable phase assemblage is liquid, garnet, and modified spinel, which is replaced by phase B above the melting temperature of modified spinel, and garnet is the liquidus phase at this pressu

ISSN:0094-8276    

DOI:10.1029/GL013i003p00181

年代:1986

数据来源: WILEY

摘要:

A paleomagnetic study of late Triassic to early Jurassic rocks from the Watchung Syncline provides useful new constraints on the complex development of the Newark Basin independent of existing structural data. A baked contact test indicates stable remanent magnetizations are primary. Results from the eastern limb of the fold are used to calculate an early Jurassic pole at Long. 115.1°E, Lat. 62.2°N (alpha 95 = 10.5°, K = 41.4) which is similar to previous Newark Basin results. After results from the western limb were corrected for folding, 32° of clockwise discordance remained between data from the western and eastern limbs. This cryptic rotation of Newark Basin strata appears to be localized to the border fault zone and may be due to the presence of left lateral secondary brittle shear zones running parallel to strata of the western limb of the Watchung Syncl

ISSN:0094-8276    

DOI:10.1029/GL013i003p00185

年代:1986

数据来源: WILEY

摘要:

The remanent magnetism (RM) for 93 specimens has been determined in 34 independently oriented samples from 20 sites at Ringgold Gap, Georgia, in the Valley and Ridge Province of the Southern Appalachians. Lithologies sampled include Middle Ordovician through Silurian fossiliferous limestones and hematitic sandstones and siltstones. The section is confined within a single thrust slice. Thermal demagnetization results indicate that hematite is the dominant RM carrier although detrital magnetite has also been identified optically in some specimens.Both normal and reversed polarities are present and the resulting paleopole is 28°N, 142°E (α95= 7.3°). This pole falls within the cluster of published Lower Paleozoic Valley and Ridge poles but rather than clarifying the distribution of poles it augments the scatter. Three factors are thought to contribute to this scatter: (1) unresolved components of rotation, possibly introduced during folding and thrust faulting, which result in declination anomalies, (2) true vertical axis tectonic rotations during deformation, and (3) insufficient knowledge of the timing of magnetization. In light of these uncertainties, caution should be exercised in constructing a Lower Paleozoic apparent polar wander path with paleopoles from the Valley and Ridge Provi

ISSN:0094-8276    

DOI:10.1029/GL013i003p00189

年代:1986

数据来源: WILEY

摘要:

Analysis of temperatures retrieved from satellite limb radiance measurements of the stratosphere and mesosphere during January‐February 1979 reveals 3 prominent waves: wave number 3 with period 2.1 days, wave number 4 with period 1.8 days, and wave number 1 with period approximately 9 days. Each of these has maximum amplitude in the equatorward shear zone of the summer mesospheric easterly jet and propagates westward. Characteristics of the 1.8 day wave number 4 mode indicate that it arises from instability of the jet. The set of three waves may comprise an interacting tria

ISSN:0094-8276    

DOI:10.1029/GL013i003p00193

年代:1986

数据来源: WILEY

摘要:

Ground‐based microwave measurements of upper atmospheric water vapor were made during late 1981 at Penn State University using the spectral line decomposition of solar microwave (22.235 GHz) radiation transmitted through the atmosphere. One measurement per day was accomplished by integrating the signal over the daylight hours from sunrise to sunset while accurately tracking the sun with a 2.4 m cassegrain parabola antenna. Preliminary retrievals for the period 13‐21 December 1983 are presented, which show reasonable agreement with recent emission microwave measureme

ISSN:0094-8276    

DOI:10.1029/GL013i003p00197

年代:1986

数据来源: WILEY

摘要:

Occultations of Io by other Galilean satellites in 1985 provide a means to locate volcanic hot spots and to model their temperatures. We have computed the expected time variations in the integral reflected and emitted radiation of the occultations as a function of wavelength (visual to 8.7µm). The best current ephemerides were used to calculate the geometry of each event as viewed from Earth. Visual reflectances were modeled from global mosaics of Io. Thermal emission from the hot spots was calculated from Voyager 1 IRIS observations and, for regions unobserved by IRIS, from a model based on the distribution of low‐albedo features. The occultations may help determine (1) the location and temperature distribution of Loki; (2) the source(s) of excess emission in the region from long 50° to 200°; and (3) the distribution of small, high‐temperature s

ISSN:0094-8276    

DOI:10.1029/GL013i003p00201

年代:1986

数据来源: WILEY