scholarly journals P-wave complexity and fault asperities: The Borrego Mountain, California, earthquake of 1968

1982 ◽  
Vol 72 (2) ◽  
pp. 413-437 ◽  
Author(s):  
John E. Ebel ◽  
Donald V. Helmberger
Keyword(s):  
Strong Motion ◽  
Source Model ◽  
P Wave ◽  
Aftershock Activity ◽  
P Waves ◽  
Deconvolution Analysis ◽  
Long Period ◽  
Short Period ◽  
Forward And Inverse Modeling ◽  
Stress Drops

Abstract Results from a synthetic seismogram analysis of the short-period P waves from the Borrego Mountain earthquake of 9 April 1968 (ML = 6.4) are used to model the strong-motion recording at El Centro. A short-period-long-period deconvolution analysis of the teleseismic P waves suggested that a two-source model would fit the data much better than the single-source model presented by Burdick and Mellman (1976). Forward and inverse modeling of the data demonstrated that two sources, each of less than 2-sec duration, the second occurring 2.2 sec after the first and both being at about 8-km depth, best fit the short-period waveforms. From this model, long-period synthetics were generated which were found to be quite compatible with the data. This source model was also used to synthesize the strong-motion SH displacement, velocity, and acceleration records from El Centro, California. The close match of synthetics and data is used to argue that short-period waveforms contain much information about asperities which play a crucial role in the near-source strong motions from an earthquake. The Borrego Mountain event probably began with the failure of a fault asperity. The evidence for this is the several-hundred-bars stress drops of the two short-period sources and the probable location of these sources in a place where there was almost no aftershock activity or postseismic creep on the fault.

scholarly journals The February 9, 1971 San Fernando earthquake: A study of source finiteness in teleseismic body waves

1978 ◽  
Vol 68 (1) ◽  
pp. 1-29 ◽  
Author(s):  
Charles A. Langston
Keyword(s):  
Near Field ◽  
Dislocation Line ◽  
Strong Motion ◽  
Body Waves ◽  
P Waves ◽  
Long Period ◽  
Short Period ◽  
Wave Forms ◽  
San Fernando ◽  
The Time Domain

abstract Teleseismic P, SV, and SH waves recorded by the WWSS and Canadian networks from the 1971 San Fernando, California earthquake (ML = 6.6) are modeled in the time domain to determine detailed features of the source as a prelude to studying the near and local field strong-motion observations. Synthetic seismograms are computed from the model of a propagating finite dislocation line source embedded in layered elastic media. The effects of source geometry and directivity are shown to be important features of the long-period observations. The most dramatic feature of the model is the requirement that the fault, which initially ruptured at a depth of 13 km as determined from pP-P times, continuously propagated toward the free surface, first on a plane dipping 53°NE, then broke over to a 29°NE dipping fault segment. This effect is clearly shown in the azimuthal variation of both long period P- and SH-wave forms. Although attenuation and interference with radiation from the remainder of the fault are possible complications, comparison of long- and short-period P and short-period pP and P waves suggest that rupture was initially bilateral, or, possibly, strongly unilateral downward, propagating to about 15 km depth. The average rupture velocity of 1.8 km/sec is well constrained from the shape of the long-period wave forms. Total seismic moment is 0.86 × 1026 dyne-cm. Implications for near-field modeling are drawn from these results.

scholarly journals The effects of tectonic release on short-period P waves from NTS explosions

1984 ◽  
Vol 74 (3) ◽  
pp. 819-842
Author(s):  
Thorne Lay ◽  
Terry C. Wallace ◽  
Don V. Helmberger
Keyword(s):  
Frequency Component ◽  
Temporal Variations ◽  
P Wave ◽  
High Frequency Component ◽  
Stress Regime ◽  
P Waves ◽  
Underground Nuclear Explosions ◽  
Long Period ◽  
Short Period ◽  
Amplitude Pattern

Abstract The first cycle (ab amplitude) of teleseismic short-period P waves from underground nuclear explosions at Pahute Mesa (NTS) show a systematic azimuthal amplitude pattern that can possibly be explained by tectonic release. The amplitudes vary by a factor of three, with diminished amplitudes being recorded at azimuths around N25°E. This azimuthal pattern has a strong sin(2φ) component and is observed, to varying degrees, for 25 Pahute Mesa events, but not for events at other sites within the NTS. Events that are known to have large tectonic release have more pronounced sin(2φ) amplitude variations. A synthesis of long-period body and surface wave investigations of tectonic release for Pahute Mesa events shows that, in general, the nonisotropic radiation is equivalent to nearly vertical, right-lateral strike-slip faulting trending from N20°W to due north. Long-period P waves at upper mantle distances demonstrate that there is a significant high-frequency component to the tectonic release. Using the long-period constraints on orientation, moment, and frequency content of the tectonic release, the expected short-period P wave effects are predicted. For models in which the downgoing P wave from the explosion triggers tectonic release within a few kilometers below the shot point, a factor of 2.5 amplitude variation with azimuth is predicted for the short-period ab amplitudes, with the lowest amplitudes expected near N25°E. Rather subtle azimuthal variations in the waveforms are expected, particulary for downward propagating ruptures, which is consistent with the absence of strong variations in the data. The occurrence of the azimuthal pattern, albeit with varying strength, for all of the Pahute Mesa events suggests a tectonic release model in which the shatterzone surrounding the explosion cavity is extended preferentially downward by driving a distributed network of faults and joints underlying the Mesa several kilometers beneath the surface. In this model, all events could have a component of tectonic release which would reflect the regional stress regime, although there may be slight spatial and temporal variations in the tectonic release contribution. Some events may trigger slip on larger throughgoing faults as well. While it is shown that tectonic release can affect teleseismic short-period signals significantly, and may contribute to the Pahute Mesa amplitude pattern, other possible explanations are considered.

Short- and long-period subevents of the 4 February 1965 Rat Islands earthquake

1984 ◽  
Vol 74 (4) ◽  
pp. 1331-1347
Author(s):  
Jim Mori
Keyword(s):  
Wave Velocity ◽  
Fault Plane ◽  
High Stress ◽  
P Wave ◽  
Long Period ◽  
P Wave Velocity ◽  
Short Period ◽  
Main Fault ◽  
The Times ◽  
Stress Drops

Abstract Short- and long-period records of the P wave of the 1965 Rat Islands earthquake were analyzed to locate subevents within the main rupture. Four subevents were identified on the short-period records in the first 100 sec and on the two long-period records in the first 30 sec. The short-period subevents cluster in an area 100 km south of the initial epicenter which appears to be off of the main fault plane, an area in which two larger aftershocks have relatively high stress drops. The long-period subevents are located 90 km west of the initial epicenter. The times and locations of the first short- and long-period subevents indicate they were triggered by a front moving near the P-wave velocity.

Azimuthal anomalies of short-period P-wave arrivals from Nahanni aftershocks, Northwest Territories, Canada, and effects of surface topography

1990 ◽  
Vol 80 (5) ◽  
pp. 1272-1283
Author(s):  
Goetz G. R. Buchbinder ◽  
R. A. W. Haddon
Keyword(s):  
Surface Topography ◽  
Northwest Territories ◽  
P Wave ◽  
Digital Data ◽  
Aftershock Activity ◽  
P Waves ◽  
Short Period ◽  
Order Of Magnitude ◽  
Large Earthquakes ◽  
Theoretical Results

Abstract Following two large earthquakes in the Northwest Territories of Canada in 1985 and one in 1988, four field surveys were undertaken to study the extensive aftershock activity. Some of the seismographs employed recorded three-component digital data, which allowed the directions of approach of short-period P-wave arrivals to be analyzed. At three stations, observed azimuthal deviations reached as much as 40° from theoretically expected azimuths as computed from the inferred hypocenters for the events. Theoretical results are presented that support the hypothesis that the observed azimuthal deviations are caused principally by local topographic slopes in the vicinity of the recording instruments. Similar theoretical results indicate that effects of local surface topography on arrival azimuths of SH and SV waves are nearly an order of magnitude less than for P waves, so that such effects will generally be unimportant in shear wave splitting studies.

High stress drops of short-period subevents from the 1968 Tokachi-Oki earthquake as observed on strong-motion records

1984 ◽  
Vol 74 (5) ◽  
pp. 1529-1544
Author(s):  
Jim Mori ◽  
Kunihiko Shimazaki
Keyword(s):  
Source Parameters ◽  
High Stress ◽  
Strong Motion ◽  
P Waves ◽  
Strong Motion Records ◽  
Source Dimensions ◽  
Short Period ◽  
High Dynamic ◽  
Stress Drops ◽  
Very High

Abstract Strong-motion records of the 1968 Tokachi-Oki earthquake were examined, and two very high stress drop subevents were identified. The first subevent had been previously located by Nagamune (1969), and the second subevent was located in this study using P waves recorded on short-period WWSSN records. Estimates of source parameters revealed small source dimensions (<1 per cent of the aftershock area) and very high dynamic and static stress drops in the kilobar range for both of the subevents. It is suggested that these subevents are important in driving the main rupture of this earthquake. The two subevents also produced the dominant accelerations on the strong-motion records, and it is shown that high-peak accelerations (150 to 200 cm/sec2) were recorded even at relatively large distances (100 to 200 km).

Synthesis of teleseismic P waves from sources near sinking lithospheric slabs

1975 ◽  
Vol 65 (6) ◽  
pp. 1667-1680
Author(s):  
Ronald W. Ward ◽  
Keiiti Aki
Keyword(s):  
Wave Amplitude ◽  
Wave Theory ◽  
P Wave ◽  
Wave Form ◽  
Shadow Zone ◽  
P Waves ◽  
Wave Source ◽  
Long Period ◽  
Short Period ◽  
Dominant Period

abstract A wave theory method is used to determine the effect of a sinking lithospheric slab on short-period and long-period waves. We consider a simplified model of the lithospheric slab with a 10 per cent velocity contrast and compute both short-period and long-period theoretical seismograms from a P-wave source located in or near the slab. For this model, the ray-theoretical amplitude agrees quite well with the short-period amplitude. In the ray-theoretical shadow zone the long-period seismograms (15- to 25-sec dominant period) typically have amplitudes 50 per cent (or greater) of the direct P-wave amplitude and exhibit wave-form broadening. Similar wave-form broadening has been attributed to the dynamics of earthquake faulting. The effect of the lithosphere on long-period waves from nearby sources must be taken into account in studies which utilize the observed variation in wave-form broadening to infer earthquake source dynamics.

The June 13, 1975 earthquake and its relationship to the New Madrid seismic zone

1977 ◽  
Vol 67 (1) ◽  
pp. 209-218
Author(s):  
R. B. Herrmann ◽  
G. W. Fischer ◽  
J. E. Zollweg
Keyword(s):  
Parameter Estimation ◽  
Seismic Moment ◽  
Strong Motion ◽  
P Wave ◽  
Eastern North America ◽  
New Madrid Seismic Zone ◽  
Seismic Zone ◽  
Long Period ◽  
Consistent Solution ◽  
New Madrid

abstract The June 13, 1975 earthquake in the New Madrid seismic zone produced the first recorded strong-motion accelerograms for an event in the region, as well as the largest recorded accelerations to date for any event in eastern North America. The peak strong-motion values obtained from an analysis of the accelerograms are the following: amax = 43 cm/sec2, vmax = 1 cm/sec and dmax = 0.05 cm for the longitudinal S88°W component; amax = 31 cm/sec2, vmax = 0.6 cm/sec and dmax = 0.01 cm for the DOWN component; amax = 64 cm/sec2, vmax = 1.6 cm/sec2, and dmax = 0.09 cm for the tangential S02°E component. Source parameter estimation using long-period surface waves, Lg spectra, P-wave first motions and the integrated accelerograms leads to a consistent solution. The seismic moment is estimated to be 4E21 dyne-cm and the corner period 0.6 sec. The corner period-seismic moment pair for this event agrees with the regional scaling of these parameters observed by Street et al. (1975).

Determination of source parameters of small earthquakes from P-wave rise time

1973 ◽  
Vol 63 (2) ◽  
pp. 599-614 ◽  
Author(s):  
M. E. O'Neill ◽  
J. H. Healy
Keyword(s):  
Rise Time ◽  
Source Parameters ◽  
P Wave ◽  
Simple Method ◽  
Zero Crossing ◽  
Basic Measurement ◽  
Earthquake Source Parameters ◽  
Short Period ◽  
Stress Drops

abstract A simple method of estimating source dimensions and stress drops of small earthquakes is presented. The basic measurement is the time from the first break to the first zero crossing on short-period seismograms. Graphs relating these measurements to rise time as a function of Q and instrument response permit an estimate of earthquake source parameters without the calculation of spectra. Tests on data from Rangely, Colorado, and Hollister, California, indicate that the method gives reasonable results.

Continuous measurements of microtremors on sediments and basement in Los Angeles, California

1993 ◽  
Vol 83 (5) ◽  
pp. 1595-1609 ◽  
Author(s):  
Hiroaki Yamanaka ◽  
Marijan Dravinski ◽  
Hiroshi Kagami
Keyword(s):  
Los Angeles ◽  
Continuous Measurement ◽  
Strong Motion ◽  
Spectral Ratio ◽  
Earthquake Ground Motion ◽  
Spectral Amplitude ◽  
Spectral Ratios ◽  
Long Period ◽  
Short Period ◽  
Deep Sediments

Abstract Continuous measurement of microtremors at two sites on basement rock and sediments was carried out in Los Angeles, California, in order to understand the fundamental characteristics of microtremors. A predominant peak with a period of about 6.5 sec was found in the microtremor spectra in both media. The spectral amplitude of the peaks varied gradually with time in a similar manner at the two sites. Their time-variant characteristics are in agreement with change in oceanic swell height observed at an oceanic buoy in the southwest of Los Angeles. This suggests that they originate from an oceanic disturbance. On the other hand, a clear daily variation of spectral amplitudes at a period of 0.3 sec indicates that short-period microtremors are caused by cultural noises. It was found that the spectral ratio of long-period microtremors between the basement and the sediments was repeatable, although the spectral amplitudes at the two sites were time-variant. The spectral ratio of the long-period microtremors was similar to that derived from strong motion records. This suggests the applicability of spectral ratios of microtremors to assess the effects of deep sediments on long-period earthquake ground motion.

scholarly journals RETRACTED ARTICLE: Estimation of the source process and forward simulation of long-period ground motion of the 2018 Hokkaido Eastern Iburi, Japan, earthquake

2019 ◽  
Vol 71 (1) ◽  
Author(s):  
Hisahiko Kubo ◽  
Asako Iwaki ◽  
Wataru Suzuki ◽  
Shin Aoi ◽  
Haruko Sekiguchi
Keyword(s):  
Ground Motion ◽  
Velocity Structure ◽  
Time Window ◽  
Waveform Inversion ◽  
Strong Motion ◽  
Source Model ◽  
Multiple Time ◽  
Velocity Models ◽  
Long Period ◽  
Slip Area

Abstract In this study, we investigate the source rupture process of the 2018 Hokkaido Eastern Iburi earthquake in Japan (MJMA 6.7) and how the ground motion can be reproduced using available source and velocity models. First, we conduct a multiple-time-window kinematic waveform inversion using strong-motion waveforms, which indicates that a large-slip area located at a depth of 25–30 km in the up-dip direction from the hypocenter was caused by a rupture propagating upward 6–12 s after its initiation. Moreover, the high-seismicity area of aftershocks did not overlap with the large-slip area. Subsequently, using the obtained source model and a three-dimensional velocity structure model, we conduct a forward long-period (< 0.5 Hz) ground-motion simulation. The simulation was able to reproduce the overall ground-motion characteristics in the sedimentary layers of the Ishikari Lowland.

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