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• We have studied the capability of elastic-wave imaging for monitoring conformance and containment in geologic carbon storage, particularly for monitoring secondary CO 2 plumes, using the waveform information of time-lapse multi-component seismic reflection data for the Kimberlina-2 models. We have described the elastic models of different secondary CO 2 plume scenarios and performed elastic-wave modeling and imaging for these models. Our results show that seismic imaging with elastic least-squares reverse-time migration of multi-component data is able to locate the secondary CO 2 plumes at different depths in the Kimberlina-2 model. With noise-free data, the time-lapse seismic images of CO 2 migration scenarios also reveal the growth of the secondary CO 2 plumes with time. We have also demonstrated that elastic-wave imaging using multi-component data can provide the relative magnitude difference in elastic properties caused by the secondary CO 2 plumes. Even with noisy data, seismic imaging using elastic LSRTM is capable of locating early stages of the secondary CO 2 plumes. Seismic noise has more impact on locating the very early stage of the secondary CO 2 plumes than those in the later stages. Our image noise analysis further suggests that the elastic-wave imaging capability decreases for the acquisition geometry with sparser shots/receivers or shorter recording offsets. The image sign-to-noise ratio is approximately proportional to the square root of the total number of seismic traces used for elastic-wave imaging. This relationship can be use to guide seismic monitoring design. Note that it is difficult to use multi-component data to accurately invert for the time-lapse change of an elastic property if its change is much smaller than those of the other elastic properties. We will study how seismic noises can affect the CO 2 detection threshold in the future. Commercial-scale geologic carbon storage requires monitoring for conformance and containment of the injected CO 2 , including secondary CO 2 plumes. Detecting and locating secondary CO 2 plumes are even more challenging than monitoring the primary CO 2 plumes. We study the capability of elastic-wave imaging for monitoring secondary CO 2 plumes with time-lapse multi-component data from 3D elastic models built using the geologic settings of the Kimberlina site located in the San Joaquin Basin, California. In the numerical simulation of CO 2 migration in these time-lapse Kimberlina-2 models, CO 2 migrates from the storage reservoir along a steeply dipping fault and forms secondary CO 2 plumes in formations at different depths. In our study, we extract a 2D slice through the location of the secondary CO 2 plumes to perform elastic-wave modeling and imaging based on numerical simulation to the elastic-wave equation. We use a finite-difference algorithm to generate time-lapse multi-component synthetic elastic-wave reflection data and employ elastic least-squares reverse-time migration to produce images of P- and S-wave velocities and density for various sizes of the secondary CO 2 plumes after CO 2 migration through the fault. Our imaging results show that, for noise-free data, elastic-wave imaging accurately locates the secondary CO 2 plumes at different depths and reveals the growth of the size of the secondary CO 2 plumes with years of CO 2 migration. The relative amplitude differences of seismic images reveal how secondary CO 2 plumes change elastic parameters differently. We further study the capability of elastic-wave imaging for monitoring the secondary CO 2 plumes using noisy synthetic data containing seismic noise extracted from a field surface seismic dataset. We evaluate elastic-wave imaging capability for monitoring secondary CO 2 plumes using different noise levels and different acquisition geometries. Our results demonstrate that elastic-wave imaging is capable of locating secondary CO 2 plumes even with strong noisy data, and a relatively higher signal-to-noise ratio (SNR) is needed to locate (or image) the secondary CO 2 plumes at earlier stages. The imaging capability decreases for sparser or shorter-offset acquisition geometry. Our results indicate that the image SNR is approximately proportional to the square root of the total trace number used for elastic-wave imaging. This relationship can be used to guide whether a denser or longer-offset acquisition geometry is worth the increase of seismic image quality for improving the capability to locate secondary CO 2 plumes. Note that multi-component data can inform us whether the time-lapse change of one elastic property is much smaller than others, but it is difficult to accurately invert for the time-lapse change of an elastic property if its change is relatively much smaller than the changes of the other elastic properties. [ABSTRACT FROM AUTHOR]

Receiver functions (RFs) from station PKD located ∼3 km SW of the San Andreas Fault (SAF) samples the Salinian terrane near Parkfield. Crustal multiples indicate a 26-km-thick crust with a VP/ VS of 1.88, which is slightly lower (1.83) for the upper and middle crust in the west. For the mid-crust, arrivals are observed at times corresponding to recently imaged seismic reflectors and may correspond to a layer of metasedimentary rocks below the base of the granitic batholith exposed at the surface. For the lower crust, RFs display strong polarity reversals with backazimuth and a change in Moho amplitude that require strong seismic anisotropy (>15 per cent) in a low velocity, high VP/ VS, possibly serpentinite or fluid filled schist layer that has a ENE dipping (∼35°) rock fabric. Similar patterns of amplitude variations and polarity reversal observed in RFs for some southern California stations located west of the SAF support the hypothesis that the cause of these data characteristics is a regionally prevalent lower crustal anisotropy. The orientation of this anisotropic fabric is inconsistent with the recent San Andreas sense of shear and is most likely a fossilized fabric of past eastward-directed (Farallon Plate) subduction. [ABSTRACT FROM AUTHOR]

We have conducted a series of cross-well experiments to continuously measure in situ temporal variations in seismic velocity at two test sites: building 64 (B64) and Richmond Field Station (RFS) of the Lawrence Berkeley National Laboratory in California. A piezoelectric source was used to generate highly repeatable signals, and a string of 24 hydrophones was used to record the signals. The B64 experiment was conducted utilizing two boreholes 17 m deep and 3 m apart for ∼ 160 h. At RFS, we collected a 36-day continuous record in a cross-borehole facility using two 70-m-deep holes separated by 30 m. With signal enhancement techniques we were able to achieve a precision of ∼6.0 nsec and ∼10 nsec in delay-time estimation from stacking of 1-hr records during the ∼7- and ∼35-day observation periods at the B64 and RFS sites, which correspond to 3 and 0.5 ppm of their travel times, respectively. Delay time measured at B64 has a variation of ∼2 µsec in the 160-hr period and shows a strong and positive correlation with the barometric pressure change at the site. At RFS, after removal of a linear trend, we find a delay-time variation of ∼2.5/µsec, which exhibits a significant negative correlation with barometric pressure. We attribute the observed correlations to stress sensitivity of seismic velocity known from laboratory studies. The positive and negative sign observed in the correlation is likely related to the expected near- and far-field effects of this stress dependence in a poroelastic medium. The stress sensitivity is estimated to be ∼10-6/ Pa and ∼10-7/Pa at the B64 and RFS site, respectively. [ABSTRACT FROM AUTHOR]

We have developed and implemented an automated moment tensor inversion procedure to determine source parameters for southern California earthquakes. The method is based upon spectral-element simulations of regional seismic wave propagation in an integrated 3D southern California velocity model. Sensitivity to source parameters is determined by numerically calculating the Fréchet derivatives required for the moment tensor inversion. We minimize a waveform misfit function, and allow limited time shifts between data and corresponding synthetics to accommodate additional 3D heterogeneity not included in our model. The technique is applied to three recent southern California earthquakes: the 9 September 2001, ML 4.2 Hollywood event, the 22 February 2003, ML 5.4 Big Bear event, and the 14 December 2001, ML 4.0 Diamond Bar event. Using about half of the available three-component data at periods of 6 sec and longer, we obtain focal mechanisms, depths, and moment magnitudes that are generally in good agreement with estimates based upon traditional body-wave and surface-wave inversions. [ABSTRACT FROM AUTHOR]

The average velocity to 30 m [Vs(30)] is a widely used parameter for classifying sites to predict their potential to amplify seismic shaking. In many cases, however, models of shallow shear-wave velocities, from which Vs(30) can be computed, do not extend to 30 m. If the data for these cases are to be used, some method of extrapolating the velocities must be devised. Four methods for doing this are described here and are illustrated using data from 135 boreholes in California for which the velocity model extends to at least 30 m. Methods using correlations between shallow velocity and Vs(30) result in significantly less bias for shallow models than the simplest method of assuming that the lowermost velocity extends to 30 m. In addition, for all methods the percent of sites misclassified is generally less than 10% and falls to negligible values for velocity models extending to at least 25 m. Although the methods using correlations do a better job on average of estimating Vs(30), the simplest method will generally result in a lower value of Vs(30) and thus yield a more conservative estimate of ground motion [which generally increases as Vs(30) decreases]. [ABSTRACT FROM AUTHOR]

The article presents information on various seismic disturbances in California during Hurricane Katrina. The beam-forming techniques were used by seismologists to back-project very low frequency seismic energy. Body waves, having double the ocean wave frequency of around 0.1 to 0.2 Hz, rattled deep through the earth from their source in shallow water. Some surface waves were detected in the Gulf of Mexico which tracked the ocean wave frequency and higher harmonics. The ocean waves from Katrina were broken to create surface and body seismic waves in shallow water.