摘要:

A microgeodetic network 22 km south east of Est. Guadalupe Victoria, Baja California Norte, installed in late May 1980, has been resurveyed in an experiment that started 12 hours after the June 9, 1980 Victoria earthquake, which had an epicenter at 10 km depth about 12 km from the network. The resurvey was complete by June 13. Both the initial observations and the resurvey were done with HP3800 distance meter equipment. Some angular control was provided with a Wild T3 theodolite. The network underwent a compressive strain of 7 ± 3 micro strain essentially parallel the Cerro Prieto fault about the time of the earthquake. Strains of this size are associated with simple dislocation models of earthquakes of this magnitude. Its direction appears to be anomalous however. This may indicate compression related to soil liquefaction processes or strain near the end of the slip plane

ISSN:0094-8276    

DOI:10.1029/GL008i006p00549

年代:1981

数据来源: WILEY

摘要:

262 P‐wave arrival times associated with 40 local events obtained from a movable array of up to eight short‐period seismographs were used to determine hypocentral parameters and an accurate three‐dimensional seismic velocity model for the Rio Grande rift zone near Socorro, New Mexico. The initial attempt to model these data resulted in a representative half‐space velocity of 5.85 ± 0.02 (1 s.d.) km/sec. No azimuthal velocity variation was found that was significantly different from the half‐space solution. The area was then subdivided at depth (4km) and into blocks one‐tenth of a degree on a side. The resulting model showed that a block in the lower layer approximately 15 km west of Socorro had an average velocity of 5.17 ± 0.11 (1 s.d.) km/sec (0.68 km/sec less than the half‐space velocity). Other blocks had smaller, but still significant, anomalies relative to the half‐space velocity. The preferred explanation for the anomalously low velocity is that this area represents a site of magmatic intrusion into the upper cru

ISSN:0094-8276    

DOI:10.1029/GL008i006p00553

年代:1981

数据来源: WILEY

摘要:

Shallow earthquakes around the southwest boundary of Long Valley caldera, west of the Hilton Creek fault, are characterized by lack of S‐waves at regional seismic network stations to the northwest, north and northeast, and P‐waves for these same station‐event combinations are deficient in frequencies higher than about 2‐3 Hz. Earthquakes east of the Hilton Creek fault and southeast of the caldera have normal P‐ and S‐wave signatures at the same stations. These effects are explained by propagation through a magma chamber in the south‐central part of Long Valley caldera, at depth greate

ISSN:0094-8276    

DOI:10.1029/GL008i006p00557

年代:1981

数据来源: WILEY

ISSN:0094-8276    

DOI:10.1029/GL008i006p00561

年代:1981

数据来源: WILEY

摘要:

The permeability of a San Andreas fault gouge is determined under confining pressures up to 220 bars; it decreases with pressure from 10 nanodarcy at 15 bars to 0.3 nanodarcy at 220 bars. These values are lower than the values determined by Morrow et al. (1981). Five different samples of fault gouge with significantly different grain‐size distributions were sheared between rock joints under confining pressures to determine the effects of grain size and constitution on the strength of the fault gouge. The strength of fault gouge clearly depends on its constitution and grain size distribution, with the coarser sandy fault gouge being stronger than the finer clayey gouge. Furthermore, the coarser gouge tends to strain harden after yielding, leading to greater strength. Thus, on the San Andreas fault, inhomogeneities in gouge materials may cause spatial variations in strength. Using the permeability determined above, we estimate that the excess pore pressure generated in the fault gouge samples during the experimental shear loading may be negligibl

ISSN:0094-8276    

DOI:10.1029/GL008i006p00565

年代:1981

数据来源: WILEY

摘要:

Spheroidal modes of elastic‐gravitational oscillation that have an energy partition dominated by shear energy in the inner core are called core modes. Recordings from the IDA gravimeter network of an earthquake in the Tonga region on June 22, 1977 have provided the first unambiguous observations of core modes. They conclusively show that, at low frequencies, the inner core has a very highQ(about 3500). They also tightly constrain the ratio of the inner core radius to the mean shear velocity to be 345s with an uncertainty of 0.5

ISSN:0094-8276    

DOI:10.1029/GL008i006p00569

年代:1981

数据来源: WILEY

ISSN:0094-8276    

DOI:10.1029/GL008i006p00572

年代:1981

数据来源: WILEY

摘要:

We determined the stability of CoSiO3relative to Co2SiO4+SiO2with reversed experiments in a piston‐cylinder apparatus. Our data at 1023, 1173, 1323, and 1473 K indicate instability of CoSiO3below 17.2, 18.0, 19.1, and 20.4 Kbars. ΔG298°and ΔH298°(from oxides) calculated from our data between 900 and 1500 K are −12.5±0.2 kJ and −8.0±0.2 kJ, respectively. The dP/dT slopes of phase transformations in Fe‐bearing systems in planetary interiors that are inferred from Co analogues may

ISSN:0094-8276    

DOI:10.1029/GL008i006p00575

年代:1981

数据来源: WILEY

摘要:

Two long cores from a magnetite‐rich gabbroic intrusion near Clam Lake, Wisconsin were studied to obtain paleopole positions to aid in determining the time of intrusion and learn more about the tectonics of the area. This intrusion was suspected to be late Precambrian in age. A.F. demagnetization above 150 oe. produced reliable remanent directions. The cores were not azimuthally oriented, therefore small circle plots were made for each sample using 12 different horizontal orientations. The best pole position was considered to be where the small circle paths crossed the Precambrian polar wander curve. This gave a normal pole at N 30° E 176° which is middle Keweenawan in age. The average inclination and declination for 14 of the 18 core sections was 35° and 288° respectively, which is consistent with aeromagnetic maps of the area. The 35° inclination is consistent with most middle Keweenawan rocks of the area, after they have been corrected for a 10° ‐ 30° tilt. This suggests that the Clam Lake area was not tilted after intrusion. Basalt dikes in the gabbro gave consistently lower inclinations, which suggest a late Keweenawan time for their

ISSN:0094-8276    

DOI:10.1029/GL008i006p00579

年代:1981

数据来源: WILEY

摘要:

The recent measurements of stratospheric H2SO4vapor concentrations using passive chemoionisation mass spectrometry are continued. This work extends the altitude range of the measurements from 23.8 to 38.9 km. The results indicate a low concentration below approximately 30 km, followed by a sharp rise to a maximum value of 1 × 107molecules cm−3at 35 km. The concentration then decreases slowly with increasing height. The results are compared with previous measurements and theoretical mode

ISSN:0094-8276    

DOI:10.1029/GL008i006p00583

年代:1981

数据来源: WILEY