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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.

Foley, S, Berger J, Orcutt JA, Vernon FL.  2010.  Advanced communications for remote ocean platforms in the coming 15 years. ( Foley S, Ed.).: American Geophysical Union, 2000 Florida Ave., N.W. Washington DC 20009 USA, [URL:] AbstractWebsite

Long-term measurements in the oceans are becoming a scientific and civil imperative that is having a profound impact on oceanography and particularly seagoing oceanography. Ocean observatories such as NSFs Ocean Observatories Initiative (OOI) and NOAAs Integrated Ocean Observing System (IOOS) are providing means for making measurements of change over decadal time scales, a practice of great importance for understanding climate variability and change as well as potential for natural disasters such as tsunamis. At the same time the costs for operating ships at sea are increasing quickly (fuel, personnel, capability) and pressure is mounting for targeted community measurements in which data collected are available openly. Both of these trends drive efforts to enhance communications at sea in coming decades. Ships are now platforms for deployment and testing of new sensors that might be later deployed at fixed observatories and observatories are increasingly common; communications to these remote sites become increasingly important. Streamed real-time data from a ship or observatory allow for rapid response to new data and greater flexibility on how the science facility can be used by the community. Cost effective transfers of large blocks of data with high reliability including surety of data return, coupled with real-time streams, allow data to be analyzed quickly by shore experts and even machine-to-machine interactions, and improve the quality of information derived from science programs. For those scientists working at sea, robust communication with shore will allow for increased contributions to ongoing programs ashore. Satellite bandwidth today is still largely too expensive for personal work by individual investigators, but bandwidth will gradually decrease in price as new spacecraft are launched and more commercial operators offer service at sea. Whether paid by the minute, byte, or month, satellite communications will make increase the quality of research by making data available to a wider audience. We shall review the current use of HiSeasNet for these purposes and present anticipated enhancements of bandwidth by government and industry for the foreseeable future.

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.

Ross, ZE, Ben-Zion Y, White MC, Vernon FL.  2016.  Analysis of earthquake body wave spectra for potency and magnitude values: implications for magnitude scaling relations. Geophysical Journal International. 207:1158-1164.   10.1093/gji/ggw327   AbstractWebsite

We develop a simple methodology for reliable automated estimation of the low-frequency asymptote in seismic body wave spectra of small to moderate local earthquakes. The procedure corrects individual P- and S-wave spectra for propagation and site effects and estimates the seismic potency from a stacked spectrum. The method is applied to > 11 000 earthquakes with local magnitudes 0 < M-L < 4 that occurred in the Southern California plate-boundary region around the San Jacinto fault zone during 2013. Moment magnitude M-w values, derived from the spectra and the scaling relation of Hanks & Kanamori, follow a Gutenberg-Richter distribution with a larger b-value (1.22) from that associated with the M-L values (0.93) for the same earthquakes. The completeness magnitude for the M-w values is 1.6 while for M-L it is 1.0. The quantity (M-w - M-L) linearly increases in the analysed magnitude range as M-L decreases. An average earthquake with M-L = 0 in the study area has an M-w of about 0.9. The developed methodology and results have important implications for earthquake source studies and statistical seismology.

Gurrola, H, Minster JB, Given H, Vernon F, Berger J, Aster R.  1990.  Analysis of High-Frequency Seismic Noise in the Western United-States and Eastern Kazakhstan. Bulletin of the Seismological Society of America. 80:951-970.Website
Lindquist, KG, Newman RL, Vernon FL.  2007.  The antelope interface to PHP and applications: Web-based real-time monitoring. Seismological Research Letters. 78:663-670.   10.1785/gssrl.78.6.663   Website
Pavlis, GL, Vernon FL.  2010.  Array processing of teleseismic body waves with the USArray. Computers & Geosciences. 36:910-920.   10.1016/j.cageo.2009.10.008   AbstractWebsite

We introduce a novel method of array processing for measuring arrival times and relative amplitudes of teleseismic body waves recorded on large aperture seismic arrays. The algorithm uses a robust stacking algorithm with three features: (1) an initial 'reference' signal is required for initial alignment by crosscorrelation; (2) a robust stacking method is used that penalizes signals that are not well matched to the stack; and (3) an iterative procedure alternates between cross-correlation with the current stack and the robust stacking algorithm. This procedure always converges in a few iterations making it well suited for interactive processing. We describe concepts behind a graphical interface developed to utilize this algorithm for processing body waves. We found it was important to compute several data quality metrics and allow the analyst to sort on these metrics. This is combined with a 'pick cutoff' function that simplifies data editing. Application of the algorithm to data from the USArray show four features of this method. (1) The program can produce superior results to that produced by a skilled analyst in approximately 1/5 of the time required for conventional interactive picking. (2) We show an illustrative example comparing residuals from S and SS for an event from northern Chile. The SS data show a remarkable +/- 10 s residual pattern across the USArray that we argue is caused by propagation approximately parallel to the subduction zones in Central and South America. (3) Quality metrics were found to be useful in identifying data problems. (4) We analyzed 50 events from the Tonga-Fiji region to compare residuals produced by this new algorithm with those measured by interactive picking. Both sets of residuals are approximately normally distributed, but corrupted by about 5% outliers. The scatter of the data estimated by waveform correlation was found to be approximately 1/2 that of the hand picked data. The outlier populations of both data sets are likely produced by cycle skips, but the distribution of hand picked data show a more diffuse departure from a Gaussian error model. (C) 2010 Elsevier Ltd. All rights reserved.

Johnson, CW, Vernon F, Nakata N, Ben-Zion Y.  2019.  Atmospheric processes modulating noise in Fairfield nodal 5 Hz geophones. Seismological Research Letters. 90:1612-1618.   10.1785/0220180383   AbstractWebsite

Atmospheric processes are documented to modulate seismic noise in Fairfield Nodal three-component geophones. Spectral analysis has shown high-amplitude signals between 40 and 50 Hz in all waveforms inspected. The changes in spectral amplitudes and frequency are found to be modified by daily variations in wind velocity and temperature, which are temporally correlated for much of the study. The wind velocity is shown to affect a wide spectral band with peak amplitudes that depend on the distance from in situ structures coupling wind energy into the shallow crust. The wind velocity increases the spectral amplitudes, most noticeably in the 40-50 Hz band; it produces a 15 Hz frequency modulation in the conditions of highest wind, with resonance frequencies up to 150 Hz. These signals likely reflect a superposition of multiple local and regional sources producing wind-generated ground motions and nonlinear wave propagation in the shallow subsurface. During periods of temperatures below 0 degrees C, a similar frequency modulation is observed, but the amplitudes are not as pronounced without the elevated wind velocity. A possible source of the continuous noise signal and the temperature-dependent frequency modulation is the spike mount that is attached to the nodal housing. The noise signals modulated by the wind and temperature variations require installation procedures in order to mitigate the effects of the contaminating noise on the geophysical processes of interest.