Compressional and Shear-Wave Velocity versus Depth Relations for Common Rock Types in Northern California

Brocher, Thomas M.

doi:10.1785/0120060403

Cited by 103 publications

(57 citation statements)

References 57 publications

(116 reference statements)

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“…2b) are present almost everywhere, with variable thickness ranging from ∼0:5 km in the western part of the plain to the ∼2:8 km near the Adriatic coasts. P-wave velocity ranges from 1:7 km=s, in the shallower part, to 2:6 km=s in the deepest part-in agreement with Faust (1951) and Brocher (2008). The PlioceneQuaternary sediments (Fig.…”

Section: Dataset and Methodssupporting

confidence: 73%

“…Other published work describes P-wave velocity as a function of depth (first 5-8 km) and geologic time for a variety of relevant geological units, but for other areas. Brocher (2008) reported relations for Holocene and Plio-Quaternary, Tertiary, and (Brocher, 2005); (c) depth-velocity (and density) profiles extracted from the 3D model at the points (P1-7) reported in Figure 2a showing the lateral variation in seismic-wave properties. In each panel, the dotted line represents V P (km=s) of the 1D model used for the simulations (see the Seismic Performance section).…”

Section: Dataset and Methodsmentioning

confidence: 99%

“…3). These profiles were derived by merging the curves from Faust (1951), Ogniben et al (1975), Brocher (2008, and R. Fantoni (personal comm., 2013). Actual velocities in individual locations of the units were cut from the standard profiles, between relevant depths.…”

Section: Dataset and Methodsmentioning

confidence: 99%

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Development and Testing of a 3D Seismic Velocity Model of the Po Plain Sedimentary Basin, Italy

Molinari

Argnani

Morelli

et al. 2015

Bulletin of the Seismological Society of America

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We built a 3D seismic model of the Po Plain and neighboring regions of northern Italy, covering altogether an area about 600 km by 300 km with an approximately 1 km spaced grid. We started by collecting an extensive and diverse set of geological and geophysical data, including seismic reflection and refraction profiles, borehole logs, and available geological information. Major geological boundaries and discontinuities have thus been identified and mapped into the model. We used kriging to interpolate the geographically sparse information into continuous surfaces delimiting geological bodies with laterally varying thickness. Seismic-wave properties have been assigned to each unit using a rule-based system and, V P , V S , and ρ derived from other studies. Sedimentary strata, although with varying levels of compaction and hence material properties, may locally reach a thickness of 15 km and give rise to significant effects in seismic-wave propagation. We have used our new model to compute the seismic response for two recent earthquakes, to test its performance. Results show that the 3D model reproduces the large amplitude and the long duration of shaking seen in the observed waveforms recorded on sediments, whereas paths outside the basin may be well fit by more homogeneous (1D) hard rock structure. We conclude that the new model is suited for simulation of wave propagation, mostly for T > 3 s, and may serve well as a constraint for earthquake location and further improvements via body-or surface-wave inversion.

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Section: Dataset and Methodssupporting

confidence: 73%

Section: Dataset and Methodsmentioning

confidence: 99%

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Development and Testing of a 3D Seismic Velocity Model of the Po Plain Sedimentary Basin, Italy

Molinari

Argnani

Morelli

et al. 2015

Bulletin of the Seismological Society of America

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“…There are different rules of the sort, which usually make a distinction between the attenuation of P-and S-waves, thus providing individual Q P and Q S values, respectively. Some rules express Q S as a polynomial function of V S and Q P as a linear function of Q S or V P (e.g., Olsen et al, 2003;Brocher, 2005Brocher, , 2008Graves, 2008). Here we use…”

Section: Attenuationmentioning

confidence: 99%

Ground-Motion Simulation and Validation of the 2008 Chino Hills, California, Earthquake Using Different Velocity Models

Taborda¹,

Bielak²

2014

Bulletin of the Seismological Society of America

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We present a set of ground-motion simulations of the 2008 M w 5.4 Chino Hills earthquake using different seismic-velocity models available for southern California. The simulations are tailored for a maximum frequency of 4 Hz and a minimum shear-wave velocity of 200 m=s. We use the community models developed by the Southern California Earthquake Center, CVM-S and CVM-H. In the case of CVM-H, we use two available alternatives, with and without considering the geotechnical layers (GTL). We compare the simulation results obtained with the models against each other and validate the synthetics with recordings obtained at more than 300 stations. The comparisons are used to gain insight into the sensitivity of the results to differences in the models and to make conclusions about the strengths of each model's description of the crustal structure and the GTL in the region. The validation is done using a goodness-of-fit (GOF) criterion. We find the GOF values show a better match at frequencies below 1 Hz, within the basins, and below 0.5 Hz in general. The models, however, do not converge at frequencies lower than 0.5 Hz, and the areas where each model leads to better results do not always coincide. The synthetics start to deviate significantly from observations at frequencies above 1 and 2 Hz, although very good agreement with data can still be found at individual locations, even at the higher frequencies. CVM-S yields the best results at frequencies up to 0.25 Hz. Our results reveal significant sensitivity of the ground motion to the differences in the structural representation of basins and shallow layers in the models. This indicates the models need to be cross referenced. We close by offering suggestions on the type of improvements that could be adopted in the future.

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“…Physical properties are assigned to rock units according to the USGS Bay Area Velocity Model (Brocher 2005;Brocher 2008). The model also includes surface topography.…”

Section: E S H M O R P H I N G F O R N O N -P L a N A R Fau Lt Smentioning

confidence: 99%

A grid-doubling finite-element technique for calculating dynamic three-dimensional spontaneous rupture on an earthquake fault

Barall¹

2009

Geophysical Journal International

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S U M M A R YWe present a new finite-element technique for calculating dynamic 3-D spontaneous rupture on an earthquake fault, which can reduce the required computational resources by a factor of six or more, without loss of accuracy. The grid-doubling technique employs small cells in a thin layer surrounding the fault. The remainder of the modelling volume is filled with larger cells, typically two or four times as large as the small cells. In the resulting non-conforming mesh, an interpolation method is used to join the thin layer of smaller cells to the volume of larger cells. Grid-doubling is effective because spontaneous rupture calculations typically require higher spatial resolution on and near the fault than elsewhere in the model volume. The technique can be applied to non-planar faults by morphing, or smoothly distorting, the entire mesh to produce the desired 3-D fault geometry. Using our FaultMod finite-element software, we have tested grid-doubling with both slip-weakening and rate-and-state friction laws, by running the SCEC/USGS 3-D dynamic rupture benchmark problems. We have also applied it to a model of the Hayward fault, Northern California, which uses realistic fault geometry and rock properties. FaultMod implements fault slip using common nodes, which represent motion common to both sides of the fault, and differential nodes, which represent motion of one side of the fault relative to the other side. We describe how to modify the traction-at-split-nodes method to work with common and differential nodes, using an implicit time stepping algorithm.The paper presents a new grid-doubling technique for dynamic 3-D spontaneous rupture calculations. This technique substantially reduces the required computational resources compared to standard finite-element techniques, without loss of accuracy.A dynamic 3-D spontaneous rupture calculation is a threedimensional numerical simulation of the physical processes that occur during an earthquake (see, e.g. Harris 2004). It is constructed by specifying the relevant physical laws, which include the elastodynamic wave equation, the constitutive equations which describe the rock properties, and the frictional equations which describe the properties of the fault. It is also necessary to specify a set of initial conditions, including the initial stresses acting on the fault. Then, the computer calculates the resulting behaviour of the system, which includes the nucleation and propagation of the earthquake rupture, and the resulting seismic waves.Such calculations are extremely computationally intensive. In finite-element approaches, space is discretized into a set of elements or cells. The standard technique is to use the same sized elements throughout all or most of the modelling volume. However, accurate modelling of fault frictional behaviour requires high spatial resolution, typically requiring an element size in the neighbourhood of 100 m or less. So, even relatively modest models may need many millions of elements. Models of that size consume so much computer...

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Compressional and Shear-Wave Velocity versus Depth Relations for Common Rock Types in Northern California

Cited by 103 publications

References 57 publications

Development and Testing of a 3D Seismic Velocity Model of the Po Plain Sedimentary Basin, Italy

Development and Testing of a 3D Seismic Velocity Model of the Po Plain Sedimentary Basin, Italy

Ground-Motion Simulation and Validation of the 2008 Chino Hills, California, Earthquake Using Different Velocity Models

A grid-doubling finite-element technique for calculating dynamic three-dimensional spontaneous rupture on an earthquake fault

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