Short-term variations in slip rate and size of prehistoric earthquakes during the past 2000 years on the northern San Jacinto fault zone, a major plate-boundary structure in southern California

Onderdonk, N.; McGill, Sally F.; Rockwell, T.

doi:10.1130/l393.1

Cited by 43 publications

(51 citation statements)

References 46 publications

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“…Our model rupture lengths are shorter than the largest events found in the paleoseismic record (Onderdonk et al, 2015;Rockwell et al, 2015), though both are inconsistent with the maximum SJF event sizes predicted by UCERF3 (Field et al, 2013). A rupture energetic enough to match the UCERF3 maximum event size would produce more slip than in our models or in the paleoseismic record and may result in ground motions strong enough to topple many of the PBRs in our study area.…”

Section: Discussionsupporting

confidence: 60%

“…The smallest event modeled is an M w 5.4; the majority of the model ruptures are in the range of M w 6.2-6.5 and do not rupture the surface. These magnitudes are consistent with historical events on the SJF; the ones that produce surface rupture at all have an average surface slip of ∼1 m, as opposed to the average ∼3 m of surface slip seen in some paleoseismic events (Onderdonk et al, 2015;Rockwell et al, 2015). Ⓔ Slip plots for these models are included in the electronic supplement to this article (Fig.…”

Section: Dynamic Modelssupporting

confidence: 60%

“…The lack of surface rupture means that these historic-type events would not appear in paleoseismic trenches. However, the paleoseismic record for both the Claremont (Onderdonk et al, 2013(Onderdonk et al, , 2015 and the Casa Loma-Clark (Rockwell et al, 2015) indicates that significantly larger events, with an average slip per event of 2.5-3 m, have occurred on each strand multiple times in the past, some close enough together in time to have possibly been a single rupture.…”

Section: Introductionmentioning

confidence: 95%

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Broadband Ground Motions from Dynamic Models of Rupture on the Northern San Jacinto Fault, and Comparison with Precariously Balanced Rocks

Lozos

Olsen

Brune

et al. 2015

Bulletin of the Seismological Society of America

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The Southern California San Jacinto fault is geometrically complex, consisting of several major strands with smaller scale complexity within each strand. The two northernmost strands, the Claremont and the Casa Loma-Clark, are separated by a 25-km-long extensional stepover with an average of 4 km separation between the strands. We use a combined modeling method to assess probable rupture and groundmotion behaviors for this stepover. First, dynamic rupture modeling on geometrically complex fault strands embedded in a state-of-the-art 3D crustal velocity model is used to generate a series of scenario earthquakes. We then use the resulting near-fault lowfrequency (< 1 Hz) ground-motion time histories to generate broadband synthetic seismograms with a hybrid approach. These synthetics are then compared with a distribution of precariously balanced rocks (PBRs) near the fault to constrain our results and assess shaking hazard for the region surrounding the fault. Our dynamic models produce sources between M w 5.4 and 6.9, with rupture limits imposed by sharp contrasts in fault stress or by geometrical barriers. The main stepover serves as a primary barrier to rupture in our model, producing event sizes that are consistent with the historical behavior of the San Jacinto fault. The largest broadband synthetics are a good match to leading ground-motion prediction equations and are generally consistent with the distribution of PBRs, none of which experience accelerations that produce toppling probabilities significantly higher than zero. Thus, although the PBRs do not rule out any of our model scenarios, they confirm that our models produce realistic rupture extents and shaking.Online Material: Figures of total slip for additional rupture models, low-frequency intensity plots, synthetic seismograms, and comparison with ground-motion prediction equations.

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Section: Discussionsupporting

confidence: 60%

Section: Dynamic Modelssupporting

confidence: 60%

Section: Introductionmentioning

confidence: 95%

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Broadband Ground Motions from Dynamic Models of Rupture on the Northern San Jacinto Fault, and Comparison with Precariously Balanced Rocks

Lozos

Olsen

Brune

et al. 2015

Bulletin of the Seismological Society of America

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“…Other smoother interpretations of the geometry of the northern SJF exist (e.g., Marliyani et al, 2013;Onderdonk et al, 2015;Rockwell et al, 2015), but we choose to use the complex end member in this study because we believe it provides the clearest illustration of how different scales of geometrical complexity may affect the rupture process.…”

Section: Fault Geometrymentioning

confidence: 98%

“…Regardless of the exact endpoints of these ruptures, it is evident that the SJF in the vicinity of the Claremont-Casa Loma stepover can fail in a series of smaller events. Paleoseismic studies on either side of the stepover also indicate that the Claremont and Casa Loma-Clark strands alike have ruptured in multiple M w 7 events (Onderdonk et al, 2015;Rockwell et al, 2015), though the temporal resolution of these data is not precise enough to determine whether these large events involved each strand individually or both at once. Dynamic rupture modeling can help assess (1) whether the barriers that lead to this apparent segmentation are geometrical or are a result of a regional or local stress field and (2) whether a through-going rupture across the stepover is possible.…”

Section: Introductionmentioning

confidence: 95%

Rupture and Ground‐Motion Models on the Northern San Jacinto Fault, Incorporating Realistic Complexity

Lozos¹,

Oglesby²,

Brune³

et al. 2015

Bulletin of the Seismological Society of America

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We use the 3D finite-element method to conduct dynamic models of rupture and resulting ground motion on the Claremont-Casa Loma stepover of the northern San Jacinto fault. We incorporate complex fault geometry (from the U.S. Geological Survey [USGS] Quaternary Faults Database; see Data and Resources), a realistic velocity structure (the Southern California Earthquake Center Community Velocity Model-S), a realistic regional stress field with an orientation taken from seismicity relocation literature, and several stochastic self-similar shear stress distributions. As we incorporate more types of complexity, the specific effects of any individual factor become less apparent within the overall rupture behavior. We also find that the distribution of high and low shear stress that arises from combining regional and stochastic stress fields has the strongest control over where the rupture terminates. Using a regional stress field alone, as well as with the combined regional and stochastic stress realization, we find that the stepover presents a significant barrier to rupture, regardless of our choice of initial nucleation point and that it is difficult for rupture to propagate the full length of either fault segment. Greater heterogeneity of stresses tends to produce shorter ruptures. Within this result, we find that the Claremont strand is more favorable for long ruptures than the Casa Loma-Clark strand. Low-frequency ground-motion intensity and distribution are controlled largely by the velocity structure rather than by stress heterogeneity. The strongest motions produced in these models are in the San Bernardino basin. Although directivity effects do contribute to the low-frequency ground-motion distribution, particularly in the near field, they are secondary to the effects of the velocity structure.Online Material: Figures of ground motions from models used to calibrate the stress conditions for dynamic rupture propagation.

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Kinematic modeling of fault slip rates using new geodetic velocities from a transect across the Pacific‐North America plate boundary through the San Bernardino Mountains, California

et al. 2015

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Campaign GPS data collected from 2002 to 2014 result in 41 new site velocities from the San Bernardino Mountains and vicinity. We combined these velocities with 93 continuous GPS velocities and 216 published velocities to obtain a velocity profile across the Pacific-North America plate boundary through the San Bernardino Mountains. We modeled the plate boundary-parallel, horizontal deformation with 5-14 parallel and one obliquely oriented screw dislocations within an elastic half-space. Our rate for the San Bernardino strand of the San Andreas Fault (6.5 ± 3.6 mm/yr) is consistent with recently published latest Quaternary rates at the 95% confidence level and is slower than our rate for the San Jacinto Fault (14.1 ± 2.9 mm/yr). Our modeled rate for all faults of the Eastern California Shear Zone (ECSZ) combined (15.7 ± 2.9 mm/yr) is faster than the summed latest Quaternary rates for these faults, even when an estimate of permanent, off-fault deformation is included. The rate discrepancy is concentrated on faults near the 1992 Landers and 1999 Hector Mine earthquakes; the geodetic and geologic rates agree within uncertainties for other faults within the ECSZ. Coupled with the observation that postearthquake deformation is faster than the pre-1992 deformation, this suggests that the ECSZ geodetic-geologic rate discrepancy is directly related to the timing and location of these earthquakes and is likely the result of viscoelastic deformation in the mantle that varies over the timescale of an earthquake cycle, rather than a redistribution of plate boundary slip at a timescale of multiple earthquake cycles or longer.

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Short-term variations in slip rate and size of prehistoric earthquakes during the past 2000 years on the northern San Jacinto fault zone, a major plate-boundary structure in southern California

Cited by 43 publications

References 46 publications

Broadband Ground Motions from Dynamic Models of Rupture on the Northern San Jacinto Fault, and Comparison with Precariously Balanced Rocks

Broadband Ground Motions from Dynamic Models of Rupture on the Northern San Jacinto Fault, and Comparison with Precariously Balanced Rocks

Rupture and Ground‐Motion Models on the Northern San Jacinto Fault, Incorporating Realistic Complexity

Kinematic modeling of fault slip rates using new geodetic velocities from a transect across the Pacific‐North America plate boundary through the San Bernardino Mountains, California

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