scholarly journals Northridge aftershocks, a source study with TERRAscope data

1997 ◽  
Vol 87 (4) ◽  
pp. 1024-1034 ◽  
Author(s):  
Xi J. Song ◽  
Donald V. Helmberger
Keyword(s):  
Wave Train ◽  
Depth Range ◽  
Long Period ◽  
Short Period ◽  
Relative Stress ◽  
Source Mechanisms ◽  
Extended Surface ◽  
San Fernando ◽  
Stress Drops ◽  
Selection Of

Abstract Broadband and long-period displacement waveforms from a selection of Northridge aftershocks recorded by the TERRAscope array are modeled to study source characteristics. Source mechanisms and moments are determined with long-period data using an algorithm developed by Zhao and Helmberger (1994). These results are compared with those by Hauksson et al. (1995) and Thio and Kanamori (1996). The width of the direct pulses at the nearest stations PAS and CALB are measured as indications of the source duration. Another measurement of the source-time functions of these earthquakes is obtained by comparing the short-period to long-period energy ratio in the data to that in the synthetics. These measurements are used to estimate the relative stress drop using a formula given by Cohn et al. (1982). The depth distribution of the relative stress drops indicates that the largest stress drops are in the depth range of 5 to 15 km for an aftershock population of 24 events. A correlation of extended surface wave train with source depth is demonstrated for paths crossing the San Fernando basin.

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.

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.

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 Broadband time domain modeling of earthquakes from Friuli, Italy

1981 ◽  
Vol 71 (4) ◽  
pp. 1215-1231
Author(s):  
John Cipar
Keyword(s):  
Time Domain ◽  
Main Shock ◽  
Waveform Inversion ◽  
High Stress ◽  
Point Sources ◽  
Domain Modeling ◽  
Long Period ◽  
Short Period ◽  
Stress Drops ◽  
Period Instruments

abstract Short-period (SP) and long-period (LP) seismograms written by the main shock and two principal aftershocks of the 1976 Friuli, Italy, earthquake sequence are modeled in the time domain using synthetic seismograms. The main shock occurred on 6 May 1976 (20h 00m, Ms = 6.5) and both aftershocks on 15 September 1976 (03h 15m, Ms = 6.0 and 09h 21m, Ms = 5.9). Source models were determined initially by trial and error and then refined using a waveform inversion program. Two point sources of radiation are required to adequately model the aftershock short-period records. For the 09h 21m aftershock, the model derived from short-period records also produces good fits to the long-period data. The seismic moment of this earthquake is found to be 0.8 to 1.0 × 1025 dyne-cm. The SP model for the 03h 15m aftershock, on the other hand, predicts long-period synthetics which do not agree with the observations. In particular, the SP moment (0.37 × 1025 dyne-cm) is about 212 times smaller than the LP moment (1 × 1025 dyne-cm). Adding a long-period component to the SP model considerably improves LP waveform and moment agreement. In the case of the main shock, a reasonable fit to the observed SP data is obtained using three point sources of radiation. However, LP synthetics computed using this model do not agree with the observations, and the SP moment (0.65 × 1025 dyne-cm) is a small fraction of the LP moment (3 to 5 × 1025 dyne-cm). Time function durations indicate that the individual events inferred from the SP records are radiated from patches of the fault having radii of 2 to 4 km and stress drops in the range 35 to 276 bars. In comparison, stress drops estimated from LP data are found to be 12 bars (main shock) and 24 bars (09h 21m aftershock). These observations suggest that the short-period instruments are sensitive to the high-frequency radiation emitted from small, high-stress drop areas on the fault plane whereas the long-period instruments record the overall motion during the earthquake.

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.

Dynamics and Stability of Locomotion for Actively Powered Simplest Walkers

2004 ◽  
Author(s):  
Koray K. Safak
Keyword(s):  
Gait Cycle ◽  
Analytical Approximation ◽  
Heel Strike ◽  
Joint Torques ◽  
Unstable Eigenvalue ◽  
Long Period ◽  
Short Period ◽  
The Stability ◽  
Selection Of

In this paper we explore methods to achieve actively powered walking on level ground using a simple 2D walker model. The walker is activated either by applying equal joint torques at hip and ankle, or by an impulse applied at toe-off immediately before heel-strike, or by the combination of both. We show that activating the walker by equal joint torques at hip and ankle on level ground is equivalent to the dynamics of the passive walker on a downhill slope. We calculate the stability of the gait cycle by an analytical approximation to the Jacobian of the walking map. Results indicate that short-period gait cycle always has an unstable eigenvalue, whereas stability of the long-period gait cycle depends on the selection of initial stance angle.

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.

Discussion following the presentation by F. Deubner

1977 ◽  
Vol 36 ◽  
pp. 69-74
Keyword(s):  
List Type ◽  
The Sun ◽  
Type Number ◽  
Harmonic Motion ◽  
Locally Excited ◽  
Long Period ◽  
Coherent Wave ◽  
Short Period ◽  
Global Modes

The discussion was separated into 3 different topics according to the separation made by the reviewer between the different periods of waves observed in the sun :1) global modes (long period oscillations) with predominantly radial harmonic motion.2) modes with large coherent - wave systems but not necessarily global excitation (300 s oscillation).3) locally excited - short period waves.

scholarly journals Isolation and Analysis of Six timeless Alleles That Cause Short- or Long-Period Circadian Rhythms in Drosophila

Genetics ◽  
2000 ◽  
Vol 156 (2) ◽  
pp. 665-675
Author(s):  
Adrian Rothenfluh ◽  
Marla Abodeely ◽  
Jeffrey L Price ◽  
Michael W Young
Keyword(s):  
Nuclear Translocation ◽  
Phase Response Curve ◽  
Fixed Number ◽  
Constant Darkness ◽  
Genetic Screens ◽  
Protein Levels ◽  
Long Period ◽  
Short Period ◽  
Molecular Oscillation ◽  
New Alleles

Abstract In genetic screens for Drosophila mutations affecting circadian locomotion rhythms, we have isolated six new alleles of the timeless (tim) gene. Two of these mutations cause short-period rhythms of 21–22 hr in constant darkness, and four result in long-period cycles of 26–28 hr. All alleles are semidominant. Studies of the genetic interactions of some of the tim alleles with period-altering period (per) mutations indicate that these interactions are close to multiplicative; a given allele changes the period length of the genetic background by a fixed percentage, rather than by a fixed number of hours. The timL1 allele was studied in molecular detail. The long behavioral period of timL1 is reflected in a lengthened molecular oscillation of per and tim RNA and protein levels. The lengthened period is partly caused by delayed nuclear translocation of TIML1 protein, shown directly by immunocytochemistry and indirectly by an analysis of the phase response curve of timL1 flies.

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