摘要:

Using data from temporary networks of portable seismographs in southern Peru, we located 888 shallow and intermediate depth events near a proposed discontinuity in the seismic zone there. These events reveal a prominent contortion, instead of a discontinuity, that trends approximately N80°E, parallel to the direction of relative plate motion. North of about 15°S, the seismic zone beneath Peru is nearly horizontal, but south of about 15.5°S, it dips at about 25°. Volcanoes lie above the more steeply dipping zone where earthquakes occur between 120 and 140 km, and the volcanic line in southern Peru stops abruptly at the contort

ISSN:0094-8276    

DOI:10.1029/GL011i001p00038

年代:1984

数据来源: WILEY

摘要:

The Agua Blanca fault is a major, trans‐peninsular, right‐lateral fault located in northern Baja California. Its WNW‐ESE orientation is markedly different from the general trend of the San Andreas‐Gulf of California fault system. From a geological point of view, the Agua Blanca fault is considered active, but there has been little significant seismic activity directly associated with it. On October 9, 1981, the onset of an earthquake swarm was detected at the Ensenada seismic station (ENX), with a S‐P time average of 2 sec. Shortly after this, an array of up to seven portable seismic stations was installed by CICESE around Todos Santos Bay. More than 180 events were recorded during the following 10 days, after which the local seismicity decreased. A second swarm consisting of 100 microearthquakes was detected between November 28 and December 5, 1981. The epicentral locations of those events recorded at four or more local stations all lie inside Todos Santos Bay. The composite fault plane solution for both swarms indicates a right‐lateral strike‐slip vertical fault with a strike of N52°W. Geological observations allow us to conclude that the seismic activity reported here is associated with the Agua Bla

ISSN:0094-8276    

DOI:10.1029/GL011i001p00042

年代:1984

数据来源: WILEY

摘要:

Fission‐track dating of minerals from the Santa Rosa Mylonite Belt and adjoining rocks of the northeastern Peninsular Ranges batholith indicates that the area was affected by a brief, but intense cooling event approximately 61 m.y. ago. Concordant ages from different mineral species suggest a minimum temperature drop of ∼120°C during this event. This rapid cooling event probably reflects major uplift and unroofing of the batholith at the beginning of the Paleocene. These new data coupled with other published isotopic data, firmly establishes that the Santa Rosa Mylonite Belt formed during the Late Cretac

ISSN:0094-8276    

DOI:10.1029/GL011i001p00046

年代:1984

数据来源: WILEY

摘要:

In agreement with Campbell (1983), Flood Area Indices (FAI) for India are interpreted as being modulated by tidal forcing at the 18.6 yr lunar nodal period. There is evidence maximum flood was approximately out of phase with nodal epoch 1898.9 whereas at epochs 1917.5, 1936,1, 1954.7, and 1973.3 maximum flood was approximately in phase. This interpretation implies that India should be experiencing widespread dryness in an interval ±2 to 3 years centered at mid‐epoch 1982

ISSN:0094-8276    

DOI:10.1029/GL011i001p00050

年代:1984

数据来源: WILEY

摘要:

Daily solar irradiance measurements in the spectral interval 120‐305 nm have been made since 6 October 1981 with an instrument on the Solar Mesosphere Explorer. The instrument operates with a spectral resolution of about 0.75 nm. Analysis of the observed data for the period 6 December 1981 to 3 June 1983 (20 solar rotations) shows that during this period there was an apparent decrease in irradiance at all wavelengths observed (−19.7% ± 9.7% at Ly‐α) but the decrease was not significantly different from zero at wavelengths longer than 210 nm. The cross correlations between daily values of the solar irradiance and 10.7 cm flux varied from 0.7 (Ly‐α) to 0.5 (210‐215 nm) and ∼0 (290‐295nm). Calculations of the % range (i.e., highest to lowest value) of the irradiance within each solar rotation showed that for Ly‐α the range varied between 6% and 30% over the 20 solar rotations studied. At longer wavelengths the % range was smaller—about 7% at 180 nm and about 2% beyond 240 nm. The percent range values indicate representative variations useful as input data for model calculations of stratosphere/mesosphere responses to short per

ISSN:0094-8276    

DOI:10.1029/GL011i001p00054

年代:1984

数据来源: WILEY

摘要:

Comparisons of the time‐averaged vertical velocity observations from the Platteville, CO, MST radar with synoptic‐scale vertical velocities computed by the adiabatic and quasi‐geostrophic omega equation methods are made for several case studies. These first results show that an MST radar can detect synoptic‐scale vertical velocities and that at Platteville the most favorable comparison occurs when the synoptic‐scale vertical velocity is large and the temporal variance of the MST radar data

ISSN:0094-8276    

DOI:10.1029/GL011i001p00057

年代:1984

数据来源: WILEY

摘要:

The UHF‐ (70.5 cm wavelength) and S‐band (10 cm wavelength) radars at NASA Goddard Space Flight Center/Wallops Flight Facility in Virginia have been used to relate lightning activity to altitude and to the reflectivity structure of a thunderstorm. Two centers of lightning flash density were found, one between 6 and 8 km altitude and another between 11 and 15 km. Our observations show a tendency for lightning to be within the high reflectivity region and ahead of it in the less intense precipitation at the leading edge of the st

ISSN:0094-8276    

DOI:10.1029/GL011i001p00061

年代:1984

数据来源: WILEY

摘要:

The steady‐state distribution of oscillation energies for raindrops was computed for a balance between input energies from collisions and dissipation by viscosity. Calculations of the oscillation responses indicates that an appreciable fraction of large raindrops (≳ 3 mm diameter) in heavy rain showers are oscillating with axis ratio changes greater than 10%. Computations of the distribution averages for the axis ratio, backscatter ratio, and ZDRindicate increasingly significant deviations from values for static raindrop shapes with increasing rain ra

ISSN:0094-8276    

DOI:10.1029/GL011i001p00065

年代:1984

数据来源: WILEY

摘要:

Tropospheric concentrations of nocturnal NO2measured at our rural site in New Zealand (45°S, 170°E) are presented. We also describe the long path spectroscopic absorption technique used. The system features a beam splitter just before the exit slit of a scanning monochromator, and the broad spectral band signal seen at a second detector is used to remove the effect of amplitude modulations caused by atmospheric flicker. A signal ratioing technique produces nearly 2 orders of magnitude improvement in this noise. With a one hour observation period detection thresholds of 20 ppt have been achieved from absorptions over a 9.2 km path. The results display a wide range of mixing ratios from the detection threshold, up to in excess of 1 ppb on isolated days. A strong absorption feature at 442.6 nm is identified as a water vapour absorption, and the absorption cross section is found to be (3.1±0.3) × 10−26cm² molecule−1at 0.5 nm re

ISSN:0094-8276    

DOI:10.1029/GL011i001p00069

年代:1984

数据来源: WILEY

摘要:

We present springtime measurements of column amounts of stratospheric nitrogen dioxide measured by ground based absorption spectroscopy from Scott Base, Antarctica (77.8°S, 166.7°E). There is a rapid build up from<1 × 1015molecules cm−2at the end of August to about 5 × 1015molecules cm−2by mid October. The period covered is the transition time between winter night, and summer day; and in general the ‘overnight’ decay of NO2is small. The decay is most significant at times when the number of hours of sunlight per day exceeds 12 hours. There are large day to day variations in column amounts which indicate that transport is a signifi

ISSN:0094-8276    

DOI:10.1029/GL011i001p00073

年代:1984

数据来源: WILEY