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).

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.

Source dimensions and stress drops of small earthquakes near Parkfield, California

1984 ◽  
Vol 74 (1) ◽  
pp. 27-40
Author(s):  
M. E. O'Neill
Keyword(s):  
Stress Drop ◽  
Small Region ◽  
Static Stress ◽  
Depth Range ◽  
Zero Crossing ◽  
Source Dimensions ◽  
Duration Magnitude ◽  
Short Period ◽  
Static Stress Drop ◽  
Stress Drops

Abstract Source dimensions and stress drops of 30 small Parkfield, California, earthquakes with coda duration magnitudes between 1.2 and 3.9 have been estimated from measurements on short-period velocity-transducer seismograms. Times from the initial onset to the first zero crossing, corrected for attenuation and instrument response, have been interpreted in terms of a circular source model in which rupture expands radially outward from a point until it stops abruptly at radius a. For each earthquake, duration magnitude MD gave an estimate of seismic moment MO and MO and a together gave an estimate of static stress drop. All 30 earthquakes are located on a 6-km-long segment of the San Andreas fault at a depth range of about 8 to 13 km. Source radius systemically increases with magnitude from about 70 m for events near MD 1.4 to about 600 m for an event of MD 3.9. Static stress drop ranges from about 2 to 30 bars and is not strongly correlated with magnitude. Static stress drop does appear to be spatially dependent; the earthquakes with stress drops greater than 20 bars are concentrated in a small region close to the hypocenter of the magnitude 512 1966 Parkfield earthquake.

scholarly journals Rupture process of the 1987 Superstition Hills earthquake from the inversion of strong-motion data

1990 ◽  
Vol 80 (5) ◽  
pp. 1079-1098 ◽  
Author(s):  
David J. Wald ◽  
Donald V. Helmberger ◽  
Stephen H. Hartzell
Keyword(s):  
Small Area ◽  
Strong Motion ◽  
Rupture Process ◽  
Imperial Valley ◽  
Strong Motion Records ◽  
Motion Data ◽  
Single Asperity ◽  
The Third ◽  
Rupture Model ◽  
Stress Drops

Abstract A pair of significant earthquakes occurred on conjugate faults in the western Imperial Valley involving the through-going Superstition Hills fault and the Elmore Ranch cross fault. The first event was located on the Elmore Ranch fault, Ms = 6.2, and the larger event on the Superstition Hills fault, Ms = 6.6. The latter event is seen as a doublet teleseismically with the amplitudes in the ratio of 1:2 and delayed by about 8 sec. This 8-sec delay is also seen in about a dozen strong-motion records. These strong-motion records are used in a constrained least-squares inversion scheme to determine the distribution of slip on a 2-D fault. Upon closer examination, the first of the doublets was found to be itself complex requiring two episodes of slip. Thus, the rupture model was allowed to have three separate subevents, treated as separate ruptures, with independent locations and start times. The best fits were obtained when all three events initiated at the northwestern end of the fault near the intersection of the cross-fault. Their respective delays are 2.1 and 8.6 sec relative to the first subevent, and their moments are 0.4, 0.9, and 3.5 × 1025 dyne-cm, which is about half of that seen teleseismically. This slip distribution suggests multi-rupturing of a single asperity with stress drops of 60, 200, and 15 bars, respectively. The first two subevents were confined to a small area around the epicenter while the third propagated 18 km southwestward, compatible with the teleseismic and afterslip observations.

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.

Source parameters and scaling relationships of small earthquakes in the northeastern Caribbean

1981 ◽  
Vol 71 (4) ◽  
pp. 1173-1190
Author(s):  
Arthur Frankel
Keyword(s):  
Seismic Moment ◽  
Dynamic Stress ◽  
Source Parameters ◽  
Earthquake Swarm ◽  
Fold Increase ◽  
Virgin Islands ◽  
Scaling Relationships ◽  
Short Period ◽  
Relative Stress ◽  
Stress Drops

abstract The seismic moments and stress drops of 23 earthquakes (1.1 ≦ M ≦ 2.4) that occurred during an earthquake swarm in the Virgin Islands were determined from the analysis of their P waveforms. The data consist of digitally recorded seismograms collected by a short-period seismic network operating in the northeastern Caribbean. The events of the swarm are particularly useful for comparing the relative stress drops of small earthquakes, because their source to receiver paths and focal mechanisms are very similar. The static stress drops calculated for these earthquakes varied from about 0.2 to 2 bars. The data clearly illustrate that the static and dynamic stress drops of these earthquakes generally increased with the size (moment) of the events. The fault radii for these shocks increased with seismic moment, but only by a factor of 2 for a 100-fold increase in seismic moment. The velocity waveforms of the larger events were systematically more impulsive than those of the smaller earthquakes. These observations imply that, for this set of earthquakes, the final fault radius is a function of the stress drop that occurs during the rupture process.

Source parameters of the Ensenada Bay earthquake swarm, Baja California, Mexico

1985 ◽  
Vol 22 (1) ◽  
pp. 126-132 ◽  
Author(s):  
Cecilio J. Rebollar
Keyword(s):  
Seismic Data ◽  
Strain Energy ◽  
High Strain ◽  
Source Parameters ◽  
Earthquake Swarm ◽  
Ground Displacement ◽  
Source Dimensions ◽  
Fault Type ◽  
Stress Drops ◽  
High Strain Energy

Seismic data collected from the Ensenada Bay earthquake swarm of late 1981 were used to calculate the spectra of ground displacement. Data from the stations of Ensenada (ENX) and Cerro Bola (CBX), at epicentral distances of 14 and 57 km, respectively, were used to evaluate source parameters. The focal depths determined for these events were less than 10 km. The focal mechanism was a strike-slip fault type, with the plane of motion striking N52°W, parallel to the Agua Blanca Fault. Seismic moments ranging from 3.44 × 1019 to 5.99 × 1020 dyn∙cm (3.44 × 1014 to 5.99 × 1015 N∙cm) were estimated for events with local magnitudes in the range 1.7–2.3. The source dimensions were found to be 186 ± 36 m and the stress drops between 3 and 66 bar (0.3 and 6.6 MPa), comparable to results obtained in previous studies of shallow events (depths <10 km). The Ensenada swarm could be attributed to a localized zone of high-strain energy at the intersection of two faults. Ratios of P to S corner frequencies were evident for only five events; they were 1.39 ± 0.38. Magnitude and seismic moment from other studies were compared with the Ensenada data in the range of magnitudes 0–3. All the data can be accommodated by log M0 = 1.5 ML + (16.9 ± 1.1). The Ensenada earthquake swarm and the Victoria earthquake swarm, which occurred in the Mexicali valley in 1978, have similar source radii and corner frequencies for the same range of seismic moments.

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.

A study of Puget Sound strong ground motion

1981 ◽  
Vol 71 (3) ◽  
pp. 883-903
Author(s):  
Charles A. Langston
Keyword(s):  
Wave Propagation ◽  
Puget Sound ◽  
Strong Motion ◽  
Complex Data ◽  
Lateral Heterogeneity ◽  
P Waves ◽  
Motion Data ◽  
Motion Models ◽  
Short Period ◽  
Strong Ground

abstract An attempt was made to model strong motion velocities and displacements from the 1965 Puget Sound earthquake. Teleseismic P waves recorded at Tumwater, Washington, were also examined to place constraints on allowable interface contrasts and to determine whether lateral heterogeneity is a major factor affecting wave propagation. Although strong motion models qualitatively showed many of the characteristics of near-vertical wave propagation in layered structures, the amplitude behavior of individual stations was quite complex. Data from Tacoma and Seattle sites attained lower velocities and acceleration compared to Olympia. The amplitude behavior is consistent with higher attenuation under Tacoma and Seattle although this is not strictly required. The short-period P data recorded at Tumwater show evidence of large velocity contrast interfaces under the station consistent with those assumed in the crustal models. The teleseismic data also indicated that dipping structure or other lateral heterogeneity is important for Olympia structure. Irrespective of these wave propagation problems, the largest single factor which has affected the level of strong ground motions in Puget Sound is the large source depth of past earthquakes. Thus, estimates of seismic hazard based on a direct interpretation of the strong motion data of the 1965 and 1949 events will be erroneously biased toward less hazard if there is potential for shallow faulting in the Puget depression.

scholarly journals Source parameters of the 2007 Noto Hanto earthquake sequence derived from strong motion records at temporary and permanent stations

2008 ◽  
Vol 60 (10) ◽  
pp. 1011-1016 ◽  
Author(s):  
Takahiro Maeda ◽  
Masayoshi Ichiyanagi ◽  
Hiroaki Takahashi ◽  
Ryo Honda ◽  
Teruhiro Yamaguchi ◽  
...  
Keyword(s):  
Source Parameters ◽  
Strong Motion ◽  
Earthquake Sequence ◽  
Strong Motion Records ◽  
Noto Hanto Earthquake ◽  
2007 Noto Hanto Earthquake
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