scholarly journals Location of earthquake swarm events near Palmdale, California, using a linear gradient velocity model

1980 ◽  
Vol 70 (6) ◽  
pp. 2145-2158
Author(s):  
Dayna Salter Drowley ◽  
Karen C. McNally
Keyword(s):  
San Andreas Fault ◽  
Earthquake Swarm ◽  
Nonlinear Least Squares ◽  
Velocity Model ◽  
Time Data ◽  
Crustal Layer ◽  
California Institute Of Technology ◽  
San Andreas ◽  
Travel Time Data ◽  
Institute Of Technology

abstract A series of small earthquakes (0.5 ≦ ML ≦ 3.0) along a 60-km segment of the San Andreas Fault in the vicinity of Palmdale, California, has been recorded since 1976 by an array operated by the California Institute of Technology. The events were analyzed in two steps. First, travel-time data from four regionally well-recorded events (ML = 2.2, 2.8, 3.0, 2.8) were inverted using a nonlinear least-squares algorithm to obtain a local velocity model consisting of an upper crustal layer with linearly increasing velocity in dipping contact with a constant velocity half-space. Hypocenters of over 150 events were relocated using this velocity model. Most of the events are clustered between the mapped traces of the San Andreas and Punchbowl faults; however, there has been a migration of activity along the San Andreas Fault. Activity which began in a 5-km cluster has expanded during a 2-yr period to fill a 60-km segment of the fault.

Interpretation of seismic reflection profiling data for the structure of the San Andreas fault zone

1983 ◽  
Vol 73 (6A) ◽  
pp. 1701-1720
Author(s):  
R. Feng ◽  
T. V. McEvilly
Keyword(s):  
Fault Zone ◽  
Seismic Reflection ◽  
San Andreas Fault ◽  
Velocity Model ◽  
Seismic Reflection Profile ◽  
Lateral Velocity ◽  
Zone Structure ◽  
Ray Method ◽  
Velocity Change ◽  
San Andreas

Abstract A seismic reflection profile crossing the San Andreas fault zone in central California was conducted in 1978. Results are complicated by the extreme lateral heterogeneity and low velocities in the fault zone. Other evidence for severe lateral velocity change across the fault zone lies in hypocenter bias and nodal plane distortion for earthquakes on the fault. Conventional interpretation and processing methods for reflection data are hard-pressed in this situation. Using the inverse ray method of May and Covey (1981), with an initial model derived from a variety of data and the impedance contrasts inferred from the preserved amplitude stacked section, an iterative inversion process yields a velocity model which, while clearly nonunique, is consistent with the various lines of evidence on the fault zone structure.

Earthquake Swarm Along the San Andreas Fault near Palmdale, Southern California, 1976 to 1977

Science ◽  
1978 ◽  
Vol 201 (4358) ◽  
pp. 814-817 ◽  
Author(s):  
K. C. MCNALLY ◽  
H. KANAMORI ◽  
J. C. PECHMANN ◽  
G. FUIS
Keyword(s):  
Southern California ◽  
San Andreas Fault ◽  
Earthquake Swarm ◽  
San Andreas

scholarly journals Three dimensional velocity structure and relocated aftershocks for the 1985 Constantine, Algeria (MS = 5.9) earthquake

1998 ◽  
Vol 41 (1) ◽  
Author(s):  
M. ou A. Bounif ◽  
C. Dorbath
Keyword(s):  
Velocity Structure ◽  
Three Dimensional ◽  
Velocity Model ◽  
P Wave ◽  
Time Data ◽  
Data Set ◽  
S Waves ◽  
Travel Time Data ◽  
Velocity Image ◽  
Local Earthquake

Local earthquake travel-time data were inverted to obtain a three dimensional tomographic image of the region centered on the 1985 Constantine earthquake. The resulting velocity model was then used to relocate the events. The tomographic data set consisted of P and S waves travel-times from 653 carefully selected aftershocks of this moderate size earthquake, recorded at 10 temporary stations. A three-dimensional P-wave velocity image to a depth of 12 km was obtained by Thurber's method. At shallower depth, the velocity contrasts reflected the differences in tectonic units. Velocities lower than 4 km/s corresponded to recent deposits, velocities higher than 5 km/s to the Constantine Neritic and the Tellian nappes. The relocation of the aftershocks indicates that most of the seismicity occured where the velocity exceeded 5.5 km/s. The aftershock distribution accurately defined the three segments involved in the main shock and led to a better understanding of the rupture process.

THREE-DIMENSIONAL GROUND MOTION SIMULATIONS FOR LARGE EARTHQUAKES ON THE SAN ANDREAS FAULT WITH DYNAMIC AND OBSERVATIONAL CONSTRAINTS

2001 ◽  
Vol 09 (03) ◽  
pp. 1203-1214 ◽  
Author(s):  
KIM B. OLSEN
Keyword(s):  
Los Angeles ◽  
Ground Motion ◽  
San Andreas Fault ◽  
Three Dimensional ◽  
Velocity Model ◽  
Staggered Grid ◽  
Near Fault ◽  
San Andreas ◽  
3D Velocity Model ◽  
Kinematic Inversion

I have simulated 0–0.5 Hz viscoelastic ground motion in Los Angeles from M 7.5 earthquakes on the San Andreas fault using a fourth-order staggered-grid finite-difference method. Two scenarios are considered: (a) a southeast propagating and (b) a northwest propagating rupture along a 170-km long stretch of the fault near Los Angeles in a 3D velocity model. The scenarios use variable slip and rise time distributions inferred from the kinematic inversion results for the 1992 M 7.3 Landers, California, earthquake. The spatially variable static slip distribution used in this study, unlike that modeled in a recent study,1 is in agreement with constraints provided by rupture dynamics. I find peak ground velocities for (a) and (b) of 49 cm/s and 67 cm/s, respectively, near the fault. The near-fault peak motions for scenario (a) are smaller compared to previous estimates from 3D modeling for both rough and smooth faults.1,2 The lower near-fault peak motions are in closer agreements with constraints from precarious rocks located near the fault. Peak velocities in Los Angeles are about 30% larger for (b) 45 cm/s compared to those for (a) 35 cm/s.

Seismicity of San Diego, 1934-1974

1977 ◽  
Vol 67 (3) ◽  
pp. 809-826
Author(s):  
Richard S. Simons
Keyword(s):  
San Diego ◽  
Great Majority ◽  
Velocity Model ◽  
California Institute Of Technology ◽  
Crustal Velocity ◽  
San Diego Bay ◽  
Crustal Velocity Model ◽  
Institute Of Technology ◽  
The City ◽  
The Rose

abstract Twelve quarry explosions in the city of San Diego have been used to determine the following crustal velocity model for the region around it: h 1 = 1.5 k m α 1 = 3.50 k m / sec β 1 = 1.90 k m / sec ⁡ h 2 = 26.5 k m α 2 = 6.35 k m / sec ⁡ β 2 = 3.65 k m / sec h 3 = ∞ α 3 = 8.00 k m / sec β 3 = 4.60 k m / sec A computer program employing this model has been used to recalculate the epicenters of all events previously located in the San Diego area, utilizing data from the California Institute of Technology seismic network as well as recent new stations within the city. Tests on the accuracy of the location process indicate that over 50 per cent of the solutions can be expected to be within 2 km of the true epicenters and that 90 per cent will be within 4 km. A total of 37 earthquakes can now be identified with some confidence as having occurred within the study area (32.5°-33.0°N, 116.75°-117.5°W) from 1934 through 1974. Some events previously thought to be earthquakes are now found to have been quarry blasts. The great majority of the earthquakes lie either offshore or less than 10 km inland, in regions of known faulting paralleling the Coronado Escarpment and the Rose Canyon fault zone. Three earthquakes are located within 2 km of the La Nacion fault. Nine of the 11 events since 1963 have taken place within or around the south end of San Diego Bay. Depths are poorly controlled, but seem to be generally less than 8 km. Magnitudes range from 2.3 to 3.7.

A detailed seismicity study of the Middle Mountain zone at Parkfield, California

1990 ◽  
Vol 80 (3) ◽  
pp. 577-588
Author(s):  
Gail K. Nishioka ◽  
Andrew J. Michael
Keyword(s):  
San Andreas Fault ◽  
Velocity Model ◽  
Strike Slip ◽  
Seismogenic Zone ◽  
Fault Plane Solutions ◽  
Motion Data ◽  
Station Corrections ◽  
The North ◽  
San Andreas ◽  
First Motion

Abstract In order to better understand the preparation zone of the predicted Parkfield earthquake, a detailed study of the seismicity at middle Mountain in the Parkfield, California, area was made using 71 digitally recorded earthquakes that located within, or close to, the Middle Mountain alert box. These earthquakes were retimed on an interactive graphics system. Based on these new arrival times, new station corrections were developed; however the data did not support changing the velocity model developed from refraction and 1966 aftershock data. The process of retiming the earthquakes and using the new station corrections reduced the rms travel-time residuals by 70 per cent to 0.025 sec, halved the location errors, and clustered the earthquakes closer to the surface trace of the San Andreas fault. The seismicity can be approximated by a plane on the scale of several kilometers, but at finer scales two clusters were discovered that show demonstrable width to the seismogenic zone. Previous workers had proposed a 5° bend in the fault at the hypocenter of the 1966 main shock on the basis of patterns in the first motion data in the 1966 aftershocks. We find that this pattern also exists in the first-motion data from 1969 to 1987, but the 5° bend was not evident in the hypocentral distribution. This suggests that a more complicated explanation is needed to explain the first-motion data. Fault plane solutions were determined for the 71 events and 69 of these were compatible with strike-slip motion on a vertical San Andreas fault. An event located in the north end of the study area co-locates with the strike-slip solutions and may be a thrust or oblique solution. The other earthquake, located 2½ kilometers northeast of the fault, has a thrust or NNE-SSW striking right lateral solution but can not be explained by a San Andreas style mechanism. Both possible solutions can be explained by structures observed in the geology.

A note on relocating the 1963 Watsonville earthquakes

1982 ◽  
Vol 72 (4) ◽  
pp. 1309-1316
Author(s):  
David G. Evans ◽  
Thomas V. McEvilly
Keyword(s):  
San Andreas Fault ◽  
Velocity Model ◽  
Earthquake Sequence ◽  
Dense Network ◽  
Network Coverage ◽  
Site Specific ◽  
San Andreas ◽  
New Locations

abstract Events in the Watsonville earthquake sequence of August and September 1963 were found by Udias (1965) not to concentrate on the main San Andreas fault break. New locations are found using a more site-specific velocity model with carefully determined station adjustments. Resulting relocated hypocenters indicate that this sequence probably does not exhibit the anomalous spatial scatter found previously. The revised locations are found to be consistent with patterns of recent seismicity, based on dense network coverage, which show a tight coincidence with the San Andreas fault.

Automated mineral analysis in TASK8

1990 ◽  
Vol 48 (2) ◽  
pp. 212-213
Author(s):  
William F. Chambers ◽  
Arthur A. Chodos ◽  
Roland C. Hagan
Keyword(s):  
National Laboratory ◽  
Control Program ◽  
Mineral Analysis ◽  
Alamos National Laboratory ◽  
Mineral Phase ◽  
Los Alamos National Laboratory ◽  
California Institute Of Technology ◽  
Mineral Phases ◽  
Letter Code ◽  
Institute Of Technology

TASK8 was designed as an electron microprobe control program with maximum flexibility and versatility, lending itself to a wide variety of applications. While using TASKS in the microprobe laboratory of the Los Alamos National Laboratory, we decided to incorporate the capability of using subroutines which perform specific end-member calculations for nearly any type of mineral phase that might be analyzed in the laboratory. This procedure minimizes the need for post-processing of the data to perform such calculations as element ratios or end-member or formula proportions. It also allows real time assessment of each data point.The use of unique “mineral codes” to specify the list of elements to be measured and the type of calculation to perform on the results was first used in the microprobe laboratory at the California Institute of Technology to optimize the analysis of mineral phases. This approach was used to create a series of subroutines in TASK8 which are called by a three letter code.

Sign in / Sign up

Export Citation Format

Share Document