Long-period ground motions and dynamic strain field of Los Angeles basin during large earthquakes

1996 ◽  
Vol 86 (5) ◽  
pp. 1417-1433
Author(s):  
T. L. Teng ◽  
J. Qu
Keyword(s):  
Los Angeles ◽  
Displacement Field ◽  
Seismic Moment ◽  
Strain Field ◽  
San Andreas Fault ◽  
Ground Motions ◽  
Dynamic Strain ◽  
Los Angeles Basin ◽  
Long Period ◽  
San Andreas

Abstract During a big earthquake along the San Andreas fault in southern California, high excitation and low attenuation of long-period (3 to 10 sec) strong ground motions will cause wave motions to propagate efficiently far from the epicentral area. These ground motions could potentially be destructive to large-dimension structures in the Los Angeles basin. We performed calculations using the surface-wave Gaussian beam method for a 3D southern California crustal structure. Displacement field as well as the associated dynamic strain field produced by large propagating ruptures along the San Andreas fault are evaluated. Results indicate that in the presence of lateral heterogeneity, focusing and multipathing interference contribute significantly to a complex pattern of the displacement field and the associated dynamic strain field. For a big event on the San Andreas fault with a seismic moment of 1.8 × 1028 dyne-cm, long-period displacement in the Los Angeles basin could reach a maximum amplitude of meters in places. Since this calculation is fast, we have evaluated the displacement field for a dense grid of points; a differentiation gives the corresponding effective horizontal dynamic strain field. At times, the maximum effective dynamic strains may reach mid-10−3 to even 10−3—high enough to be of engineering concern. This computational result probably gives the upper bound values due to the large source assumed. For events of smaller seismic moment release along less extensive ruptures, these results can easily be scaled down proportionally. Different scenarios are considered in this study with different slip distributions. It is found that with a given seismic moment, a more evenly distributed fault slip over the rupture surface will result in lower peak values on both displacements and dynamic strains. Our displacement results give similar values to those obtained by Kanamori using empirical Green's functions but substantially higher than Bouchon and Aki's results.

Three-dimensional finite-difference modeling of the San Andreas fault: Source parameterization and ground-motion levels

1998 ◽  
Vol 88 (4) ◽  
pp. 881-897
Author(s):  
Robert W. Graves
Keyword(s):  
Los Angeles ◽  
Ground Motion ◽  
Rise Time ◽  
Seismic Moment ◽  
Slip Distribution ◽  
Los Angeles Basin ◽  
Near Fault ◽  
Long Period ◽  
San Andreas ◽  
Fault Region

Abstract Olsen et al. (1995) recently simulated an Mw 7.75 earthquake on the San Andreas fault, predicting long-period (T > 2.5 sec) ground velocities of 140 cm/sec in the Los Angeles basin, about 60 km from the fault. These motions are much larger than estimates derived from empirical relations or other numerical simulations. Standard area-magnitude relations predict that the 170 × 16 km fault used in the simulations would produce an Mw 7.5 earthquake, giving a moment of 2.0 × 1027 dyne-cm, which is 2.4 times smaller than the moment used by Olsen et al. (1995). Further, self-similar scaling predicts a rise time of 3 sec for an Mw 7.75 event and 2.2 sec for an Mw 7.5 event. The filtered impulse slip function used by Olsen et al. (1995) has an effective rise time of 1.6 sec, yielding a response that is about 2 times larger than expected for periods less than 5 sec. This combination of high seismic moment and short rise time, along with the use of a uniform slip distribution, leads to the extreme ground-motion levels predicted by Olsen et al. (1995). To quantify the sensitivity of the long-period ground-motion response to source parameterization, we have performed 3D finite-difference (FD) simulations using various combinations of seismic moment, source rise time, and slip heterogeneity. These calculations incorporate the same grid dimensions, fault size, and bandwidth employed by Olsen et al. (1995). With a moment of 2.0 ՠ1027 dyne-cm, a rise time of 2 sec, and a smoothly heterogeneous slip distribution, we simulate peak long-period ground velocities of 155 cm/sec in the near-fault region and 40 cm/sec in the Los Angeles basin. These values are much closer to (although still higher than) empirical predictions. A uniform slip distribution produces the largest peak motions, both in the near-fault region and in the Los Angeles basin, whereas a rough asperity slip distribution noticeably reduces the maximum near-fault ground velocities. Our results indicate that the accurate simulation of long-period ground motions requires a realistic source parameterization, including appropriate choices of seismic moment and rise time, as well as the use of spatial and temporal variations in slip distribution.

scholarly journals A revised position for the primary strand of the Pleistocene-Holocene San Andreas fault in southern California

2021 ◽  
Vol 7 (13) ◽  
pp. eaaz5691
Author(s):  
Kimberly Blisniuk ◽  
Katherine Scharer ◽  
Warren D. Sharp ◽  
Roland Burgmann ◽  
Colin Amos ◽  
...  
Keyword(s):  
Los Angeles ◽  
Southern California ◽  
San Andreas Fault ◽  
Slip Rate ◽  
Large Magnitude ◽  
Slip Rates ◽  
San Andreas ◽  
The Pacific ◽  
Large Earthquakes ◽  
Dependent Probability

The San Andreas fault has the highest calculated time-dependent probability for large-magnitude earthquakes in southern California. However, where the fault is multistranded east of the Los Angeles metropolitan area, it has been uncertain which strand has the fastest slip rate and, therefore, which has the highest probability of a destructive earthquake. Reconstruction of offset Pleistocene-Holocene landforms dated using the uranium-thorium soil carbonate and beryllium-10 surface exposure techniques indicates slip rates of 24.1 ± 3 millimeter per year for the San Andreas fault, with 21.6 ± 2 and 2.5 ± 1 millimeters per year for the Mission Creek and Banning strands, respectively. These data establish the Mission Creek strand as the primary fault bounding the Pacific and North American plates at this latitude and imply that 6 to 9 meters of elastic strain has accumulated along the fault since the most recent surface-rupturing earthquake, highlighting the potential for large earthquakes along this strand.

scholarly journals Dynamic models of earthquake rupture along branch faults of the eastern San Gorgonio Pass region in California using complex fault structure

Geosphere ◽  
2020 ◽  
Vol 16 (2) ◽  
pp. 474-489 ◽  
Author(s):  
Roby Douilly ◽  
David D. Oglesby ◽  
Michele L. Cooke ◽  
Jennifer L. Hatch
Keyword(s):  
Finite Element ◽  
Los Angeles ◽  
Southern California ◽  
San Andreas Fault ◽  
Recurrence Time ◽  
Fault Geometry ◽  
Regional Stress ◽  
Coachella Valley ◽  
San Andreas ◽  
Valley Segment

Abstract Geologic data suggest that the Coachella Valley segment of the southern San Andreas fault (southern California, USA) is past its average recurrence time period. At its northern edge, this right-lateral fault segment branches into the Mission Creek and Banning strands of the San Andreas fault. Depending on how rupture propagates through this region, there is the possibility of a throughgoing rupture that could lead to the channeling of damaging seismic energy into the Los Angeles Basin. The fault structures and potential rupture scenarios on these two strands differ significantly, which highlights the need to determine which strand provides a more likely rupture path and the circumstances that control this rupture path. In this study, we examine the effect of different assumptions about fault geometry and initial stress pattern on the dynamic rupture process to test multiple rupture scenarios and thus investigate the most likely path(s) of a rupture that starts on the Coachella Valley segment. We consider three types of fault geometry based on the Southern California Earthquake Center Community Fault Model, and we create a three-dimensional finite-element mesh for each of them. These three meshes are then incorporated into the finite-element method code FaultMod to compute a physical model for the rupture dynamics. We use a slip-weakening friction law, and consider different assumptions of background stress, such as constant tractions and regional stress regimes with different orientations. Both the constant and regional stress distributions show that rupture from the Coachella Valley segment is more likely to branch to the Mission Creek than to the Banning fault strand. The fault connectivity at this branch system seems to have a significant impact on the likelihood of a throughgoing rupture, with potentially significant impacts for ground motion and seismic hazard both locally and in the greater Los Angeles metropolitan area.

Measurements of the strain field associated with episodic creep events on the San Andreas Fault at San Juan Bautista, California

1994 ◽  
Vol 99 (B3) ◽  
pp. 4559-4565 ◽  
Author(s):  
M. T. Gladwin ◽  
R. L. Gwyther ◽  
R. H. G. Hart ◽  
K. S. Breckenridge
Keyword(s):  
Strain Field ◽  
San Andreas Fault ◽  
San Juan ◽  
San Andreas ◽  
San Juan Bautista

Basin waves on a seafloor recording of the 1990 Upland, California, earthquake: Implications for ground motions from a larger earthquake

1999 ◽  
Vol 89 (1) ◽  
pp. 317-324
Author(s):  
David M. Boore
Keyword(s):  
Time Series ◽  
Wave Propagation ◽  
Los Angeles ◽  
Surface Waves ◽  
Ground Motions ◽  
Response Spectra ◽  
Theoretical Models ◽  
Regression Equations ◽  
Los Angeles Basin ◽  
Basin Response

Abstract The velocity and displacement time series from a recording on the seafloor at 74 km from the 1990 Upland earthquake (M = 5.6) are dominated by late-arriving waves with periods of 6 to 7 sec. These waves are probably surface waves traveling across the Los Angeles basin. Response spectra for the recording are in agreement with predictions from empirical regression equations and theoretical models for periods less than about 1 sec but are significantly larger than those predictions for longer periods. The longer-period spectral amplitudes are controlled by the late-arriving waves, which are not included in the theoretical models and are underrepresented in the data used in the empirical analyses. When the motions are scaled to larger magnitude, the results are in general agreement with simulations of wave propagation in the Los Angeles basin by Graves (1998).

scholarly journals Performance of Two 18-Story Steel Moment-Frame Buildings in Southern California during Two Large Simulated San Andreas Earthquakes

2006 ◽  
Vol 22 (4) ◽  
pp. 1035-1061 ◽  
Author(s):  
Swaminathan Krishnan ◽  
Chen Ji ◽  
Dimitri Komatitsch ◽  
Jeroen Tromp
Keyword(s):  
Los Angeles ◽  
Southern California ◽  
Building Code ◽  
Los Angeles Basin ◽  
Moment Frame ◽  
Steel Moment Frame ◽  
Existing Building ◽  
San Andreas ◽  
Frame Buildings ◽  
San Fernando

Using state-of-the-art computational tools in seismology and structural engineering, validated using data from the Mw=6.7 January 1994 Northridge earthquake, we determine the damage to two 18-story steel moment-frame buildings, one existing and one new, located in southern California due to ground motions from two hypothetical magnitude 7.9 earthquakes on the San Andreas Fault. The new building has the same configuration as the existing building but has been redesigned to current building code standards. Two cases are considered: rupture initiating at Parkfield and propagating from north to south, and rupture propagating from south to north and terminating at Parkfield. Severe damage occurs in these buildings at many locations in the region in the north-to-south rupture scenario. Peak velocities of 1 m.s−1 and 2 m.s−1 occur in the Los Angeles Basin and San Fernando Valley, respectively, while the corresponding peak displacements are about 1 m and 2 m, respectively. Peak interstory drifts in the two buildings exceed 0.10 and 0.06 in many areas of the San Fernando Valley and the Los Angeles Basin, respectively. The redesigned building performs significantly better than the existing building; however, its improved design based on the 1997 Uniform Building Code is still not adequate to prevent serious damage. The results from the south-to-north scenario are not as alarming, although damage is serious enough to cause significant business interruption and compromise life safety.

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