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Kane, DL, Prieto GA, Vernon FL, Shearer PM.  2011.  Quantifying Seismic Source Parameter Uncertainties. Bulletin of the Seismological Society of America. 101:535-543.   10.1785/0120100166   AbstractWebsite

We use data from a small aperture array in southern California to quantify variations in source parameter estimates at closely spaced stations (distances ranging from similar to 7 to 350 m) to provide constraints on parameter uncertainties. Many studies do not consider uncertainties in these estimates even though they can be significant and have important implications for studies of earthquake source physics. Here, we estimate seismic source parameters in the frequency domain using empirical Green's function (EGF) methods to remove effects of the travel paths between earthquakes and their recording stations. We examine uncertainties in our estimates by quantifying the resulting distributions over all stations in the array. For coseismic stress drop estimates, we find that minimum uncertainties of similar to 30% of the estimate can be expected. To test the robustness of our results, we explore variations of the dataset using different groupings of stations, different source regions, and different EGF earthquakes. Although these differences affect our absolute estimates of stress drop, they do not greatly influence the spread in our resulting estimates. These sensitivity tests show that station selection is not the primary contribution to the uncertainties in our parameter estimates for single stations. We conclude that establishing reliable methods of estimating uncertainties in source parameter estimates (including corner frequencies, source durations, and coseismic static stress drops) is essential, particularly when the results are used in the comparisons among different studies over a range of earthquake magnitudes and locations.

Kane, DL, Shearer PM, Goertz-Allmann BP, Vernon FL.  2013.  Rupture directivity of small earthquakes at Parkfield. Journal of Geophysical Research-Solid Earth. 118:212-221.   10.1029/2012jb009675   AbstractWebsite

Theoretical modeling of strike-slip ruptures along a bimaterial interface suggests that earthquakes initiating on the interface will have a preferred rupture direction. We test this model with 450 small earthquakes (2 < M < 5) from Parkfield, California, to look for evidence of consistent rupture directivity along the San Andreas Fault. We analyze azimuthal variations in earthquake source spectra after applying an iterative correction for wave propagation effects. Our approach avoids directly modeling source spectra because these models generally assume symmetric rupture; instead, we look for azimuthal variations in the amplitudes of the source spectra over specified frequency bands. Our overall results show similar proportions of events exhibiting characteristics of rupture directivity toward either the southeast or northwest. However, the proportion of events with southeast rupture directivity increases as we limit the data set to larger magnitudes, with 70% of the 46 events M > 3 exhibiting southeast rupture characteristics. Some spatial and temporal variability in rupture directivity is also apparent. We observe a higher proportion of northwest directivity ruptures following the 2004 M 6 Parkfield earthquake, which ruptured toward the northwest. Our results are generally consistent with the preferred southeast rupture directivity model but suggest that directivity is likely due to several contributing factors. Citation: Kane, D. L., P. M. Shearer, B. P. Goertz-Allmann, and F. L. Vernon (2013), Rupture directivity of small earthquakes at Parkfield, J. Geophys. Res. Solid Earth, 118, 212-221, doi: 10.1029/2012JB009675.

Kappus, ME, Vernon FL.  1991.  Acoustic Signature of Thunder from Seismic Records. Journal of Geophysical Research-Atmospheres. 96:10989-11006.   10.1029/91jd00789   AbstractWebsite

Thunder, the sound wave through the air associated with lightning, transfers sufficient energy to the ground to trigger seismometers set to record regional earthquakes. The acoustic signature recorded on seismometers, in the form of ground velocity as a function of time, contains the same type features as pressure variations recorded with microphones in air. At a seismic station in Kislovodsk, USSR, a nearly direct lightning strike caused electronic failure of borehole instruments while leaving a brief impulsive acoustic signature on the surface instruments. The peak frequency of 25-55 Hz is consistent with previously published values for cloud-to-ground lightning strikes, but spectra from this station are contaminated by very strong wind noise in this band. A thunderstorm near a similar station in Karasu triggered more than a dozen records of individual lightning strikes during a 2-hour period. The spectra for these events are fairly broadband, with peaks at low frequencies, varying from 6 to 13 Hz. The spectra were all computed by multitaper analysis, which deals appropriately with the nonstationary thunder signal. These independent measurements of low-frequency peaks corroborate the occasional occurrences in traditional microphone records, but a theory concerning the physical mechanism to account for them is still in question. Examined separately, the individual claps in each record have similar frequency distributions, discounting a need for multiple mechanisms to explain different phases of the thunder sequence. Particle motion, determined from polarization analysis of the three-component records, is predominantly vertical downward, with smaller horizontal components indicative of the direction to the lightning bolt. In three of the records the azimuth to the lightning bolt changes with time, confirming a significant horizontal component to the lightning channel itself.

Kilb, D, Keen CS, Newman RL, Kent GM, Sandwell DT, Vernon FL, Johnson CL, Orcutt JA.  2003.  The Visualization Center at Scripps Institution of Oceanography: Education and Outreach. Seismological Research Letters. 74:641-648. AbstractWebsite

The immersive environment of the Visualization Center at Scripps, coupled with the presentation of current seismological research, has great education and outreach potential. Since its March 2002 opening, the Visualization Center at Scripps has had more than 2,500 visitors, and numerous virtual visitors have explored our Web pages, which include streaming QuickTime movies of geophysical data, tutorials on how to use SGI/Mac/Windows registered visualization software, and examples of visualizations developed by SIO researchers and faculty members (http://siovizcenter.ucsd.edu/library.shtml). We will continue to expand the use of the Visualization Center at Scripps for K-12 and informal education, and to use the center to supply geophysical data sets, movies, and research results to as large a group of educators as possible. Our goal is to develop more sustained K-12 educational programs and to generate assessments of the center's programs and the educational products created at the Center.

Kilb, D, Biasi G, Anderson J, Brune J, Peng ZG, Vernon FL.  2012.  A Comparison of Spectral Parameter Kappa from Small and Moderate Earthquakes Using Southern California ANZA Seismic Network Data. Bulletin of the Seismological Society of America. 102:284-300.   10.1785/0120100309   AbstractWebsite

Kappa is a one-parameter estimator of the spectral amplitude decay with frequency of a seismogram. Low values (similar to 5 ms) indicate limited attenuation of high-frequency energy whereas higher values (similar to 40 ms) indicate high-frequency energy has been removed. Kappa is often assumed to be a site term and used in seismic designs. We address two key questions about kappa: (1) how to identify source, path, and site contributions to kappa; and (2) can kappa estimates from smaller earthquakes, and more readily accessible weak- motion recordings, be reasonably extrapolated to estimate kappa of larger earthquakes? The use of small earthquakes (M-L < 1) presents many challenges and requires new approaches. We develop estimates of kappa for seismograms from 1137 small earthquakes recorded by the ANZA seismic network in southern California, and compare these to results from the stronger recorded shaking generated by 43 M-L > 3.5 earthquakes inside the network. We find kappa from small earthquakes predicts the relative values of kappa for larger earthquakes (e.g., measurements at stations PFO and KNW are small compared with those at stations TRO and SND). For the SND and TRO data, however, kappa values from small earthquakes overpredict those from moderate and large earthquakes. Site effects are the most important contributor to kappa estimates, but the scatter within kappa measurements at a given station is likely caused by a significant contribution from near the source, perhaps related to near-source scattering. Because of this source-side variability, care is recommended in using individual small events as Green's functions to study source-time effects of moderate and large events.

Kilb, D, Newman RL, Vernon FL, Eakins JA, Ziegler L, Bowen J, Otero J.  2003.  Education and outreach based on data from the Anza seismic network in Southern California. Seismological Research Letters. 74( Mellors RJ, Wald L, Eds.).:522-528., El Cerrito, CA, United States (USA): Seismological Society of America, El Cerrito, CAWebsite
Kilb, D, Martynov VG, Vernon FL.  2007.  Aftershock detection thresholds as a function of time: Results from the ANZA seismic network following the 31 October 2001 M-L 5.1 ANZA, California, earthquake. Bulletin of the Seismological Society of America. 97:780-792.   10.1785/0120060116   AbstractWebsite

We examine aftershock detectability thresholds for events in the initial part of the 31 October 2001, M-L 5.1 sequence in southern California. This sequence occurred directly below the broadband ANZA seismic network, which recorded continuous waveform data at 13 azimuthally well-distributed stations within the study region (seven had epicentral distances < 20 km). Of the 608 aftershocks (0 < ML < similar to 2.8) in the initial 2 hr of this sequence, the first five aftershocks recorded were only identifiable at stations within 30 km after applying a high-pass filter. Using a cluster (radius <= 1.1 km) of 200 representative aftershocks, we track the maximum seismogram amplitude versus earthquake magnitude. This relationship helps us quantify the visibility of aftershocks within the mainshock coda and assess our detection capabilities. We estimate that detectable aftershocks within the mainshock coda include (1) those over magnitude similar to 3 that are within 15 km of the network centroid that occur 12 sec or more into the sequence, and (2) those over magnitude similar to 2 that are within 30 km of the centroid of the network that occur 60 see or more into the sequence. We find a lack of large aftershocks in this sequence. The largest aftershock (M-L similar to 2.8) is substantially smaller than the mainshock (M-L 5.1). We suggest this relatively large-magnitude differential is dictated by a combination of factors that includes complexity of the San Jacinto fault system and the lack of large earthquakes in the region in the past similar to 20 years.

Kurzon, I, Vernon FL, Rosenberger A, Ben-Zion Y.  2014.  Real-time automatic detectors of P and S waves using singular value decomposition. Bulletin of the Seismological Society of America. 104:1696-1708.   10.1785/0120130295   AbstractWebsite

We implement a new method for automatic detection of P and S phases using singular value decomposition (SVD) analysis. The method is based on the real-time iteration algorithm of Rosenberger (2010) for the SVD of three-component seismograms. The algorithm identifies the apparent incidence angle by applying SVD and separates the waveforms into their P and S components. We apply the algorithm to filtered waveforms and then either set detectors on the incidence angle and singular values or apply signal-to-noise ratio (SNR) detectors for P and S picking on the filtered and SVD-separated channels. The Anza Seismic Network and the recent portable deployment in the San Jacinto fault zone area provide a very dense seismic network for testing the detection algorithm in a diverse setting, including events with different source mechanisms, stations with different site characteristics, and ray paths that diverge from the approximation used in the SVD algorithm. A 2-30 Hz Butterworth band-pass filter gives the best performance for a large variety of events and stations. We use the SVD detectors on many events and present results from the complex and intense aftershock sequence of the M-w 5.2 June 2005 event. This sequence was thoroughly reviewed by several analysts, identifying 294 events in the first hour, all located in a dense cluster around the mainshock. We used this dataset to fine-tune the automatic SVD detection, association, and location, achieving a 37% automatic identification and location of events. All detected events fall within the dense cluster, and there are no false events. An ordinary SNR detector does not exceed 11% success and has a wider spread of locations (not within the reviewed cluster). The preknowledge of the phases picked ( P or S) by the SVD detectors significantly reduces the noise created by phase-blind SNR detectors.