The Strong Motion Earthquake Data Values of Digitized Strong-Motion Accelerograms is a database of over 15,000 digitized and processed accelerograph records from 1933 to 1994. Data were obtained from a variety of structural and geologic environments. Most of the data are available in three levels of processed files. The first type of file contains raw (uncorrected) time, history data points digitized from the analog accelerogram. The second is a filtered, instrument corrected version of the time, history data. This file also contains calculated velocities and displacements obtained by the integration and double integration of the corrected accelerations. The third type of file includes the calculated Fourier and response spectra data. The data are from the United States, Algeria, Argentina, Armenia, Australia, Bulgaria, Canada, Chile, China, El Salvador, Fiji, Germany, Greece, India, Iran, Italy, Japan, Mexico, New Zealand, Nicaragua, Papua New Guinea, Peru, Portugal, Romania, Spain, Taiwan, Turkey, and Uzbekistan. This database is static and is no longer being updated.

On August 24, 2021, the U.S. Geological Survey conducted a high-resolution seismic survey between two strong-motion recording stations located at the Veterans Affairs Medical Center (VAMC) in the City of Menlo Park, San Mateo County, California. The stations are National Strong Motion Project Station (NSMP) 1849 in VAMC building 332 and NSMP Station 1870 in VAMC building 334. The primary goals of the seismic survey are to better understand the potential for amplified ground shaking, to evaluate lateral variability in shear-wave velocity, and to calculate time-averaged shear-wave velocity in the upper 30 m of the subsurface (Vs30) at this site using refraction tomography and multichannel analysis of surface waves (MASW) methods.

In May 2015, we acquired high-resolution seismic profiles near six strong motion instruments located in Napa and Solano Counties, California. These strong motion instruments recorded horizontal peak accelerations (PGAs) from 0.329g to 0.611g, which were among the highest recorded in the Napa area during the 24 August 2014 Mw 6.0 South Napa Earthquake. Our goal is to measure the seismic velocities of the underlying geologic material at each strong motion site using P- and S-wave refraction tomography and analysis of surface waves, especially in the upper 30 m of the subsurface.

The U.S. Geological Survey acquired high-resolution P- and S-wave seismic data across the Frijoles Fault strand of the San Gregorio Fault Zone (SGFZ) at northern Año Nuevo, California in 2012. SGFZ is a right-lateral fault system that is mainly offshore, and prior studies provide highly variable slip estimates, which indicates uncertainty about the seismic hazard it poses. Therefore, the primary goal of the seismic survey was to better understand the structure and geometry of the onshore section of the Frijoles Fault strand of the SGFZ. We deployed 118 geophones (channels) at 5-m spacing along a linear profile centered on the mapped surface trace of the Frijoles Fault and co-located active P- and S-wave sources at ~1-m offset from the geophones. Channel numbers increase from west to east along the profile. We generated P-waves using either a seisgun (www.utep.edu/science/ssf/Manuals/betsy_seisgun.pdf, accessed August 2022) or an accelerated weight-drop and S-waves by horizontally striking an aluminum block on both sides with a sledgehammer. We first deployed vertical-component geophones (40-Hz, SercelTM L40A, sensitivity of 22.34 volts/meter/second) to record P-wave sources, after which we replaced the vertical-component geophones with horizontal-component geophones (4.5-Hz, SercelTM L28-LBH, sensitivity of 31.3 volts/meter/second) to record S-wave sources. Refraction cables connected all geophones to two 60-channel Geometrics Stratavisor NX-60TM seismographs with 24-bit analog-to-digital converters. Each shot was recorded at a 0.5-ms sampling rate for two seconds, with data recording at 100 ms before the actual time of the shot. This data release provides the metadata needed to utilize the seismic data. Data Format and Files We combined each seismic trace for a given shot time into a shot gather, and the traces in each shot gather are ordered by channel numbers (1-118) based on the position of the geophones along the profile. Furthermore, we assigned a unique field number (FFID) to each shot gather, and we combined the shot gathers recorded from both seismographs into two SEG-Y files (Barry et al., 1975), 78023.segy (channels 1 to 60) and marine.segy (channels 61 to 118), which are stored in big-Endian, 4-byte IBM-floating-point format (format code 1). Data samples are in millivolts and can be converted to velocity using the geophone sensitivity values. Metadata for all profiles are contained in two text files and one xml file: PIE12.setup.csv, PIE12.location.csv, and PIE12Metadata.xml. The setup file describes the identification of shots recorded by the two seismographs, channel number, recording stations (geophones), and the source type for both SEG-Y files. The location file describes the channel number, latitude, and longitude of all geophone locations. Reference Barry, K.M., Cavers, D.A., and Kneale, C.W., 1975, Recommended standards for digital tape formats: Geophysics, vol. 40, no. 2, p. 344-352, doi: 10.1190/1.1440530.

This data release includes geodetic time series from high-rate GPS instruments recording 4 earthquakes co-seismically in the near-field – the 2010 Maule, Chile earthquake; the 2012 Nicoya, Costa Rica earthquake; the 2014 Iquique, Chile earthquake; and the 2015 Gorkha, Nepal earthquake. For each earthquake, data (sac files, 1 Hz sampling, ~2-3 minutes around the earthquake origin time) are included in a separate folder. Each sac file provides a time series of ground displacement from the earthquake as recorded at that station. The location of each station is listed in the relevant earthquake file in the “_station_info” folder.

In May 2019, the U.S. Geological Survey acquired high resolution P- and S-wave seismic data near six seismic network recording stations in San Bernardino County, California: Southern California Seismic Network CI.CLT Calelectic, CI.MLS Mira Loma, CI.CJM Cajon Mountain and CI.HLN Highland; California Strong Motion Instrumentation Program station CE.23542; and US National Strong-Motion Network station NP.5326 (Figure 1). The primary goals of the seismic survey were to better understand the potential for amplified ground shaking, to evaluate lateral variability in shear-wave velocity, and to calculate Vs30 at these sites. We deployed up to 67 DTCC SmartSolo 3-component seismometer systems ("nodes") at 2-m spacing along six linear arrays and collocated P- and S-wave sources at ~1-m offset from the nodes. We generated active-source P-waves using a 3.5-kg sledgehammer and steel plate combination. Active-source S-waves were generated by horizontally striking an aluminum block with a 3.5-kg sledgehammer. SmartSolo nodes are standalone seismometers with 3-component sensors (5-Hz corner frequency and sensitivity of 76.7 volts/meter/second), battery, and built-in GPS to record location and time. The nodes recorded seismic data continuously at a 0.5-ms sampling rate, and shot timing was recorded by GPS event capture hardware to precisely determine the shot times. For some individual surveys, the nodes were buried a few inches below the ground surface to reduce noise. This report provides the metadata needed to utilize the seismic data. Acknowledgements: We thank Garet Huddleston, Dan Langermann, Carolyn Stieban, Zhenning Ma, Luther Strayer, and Chris Green for assistance in data acquisition. Reference: Barry, K.M., Cavers, D.A. and Kneale, C.W., 1975, Recommended standards for digital tape formats: Geophysics, vol. 40, no. 2, p. 344-352.

In August 2017, the U.S. Geological Survey acquired high-resolution P- and S-wave seismic data near six Southern California Seismic Network (SCSN) recording stations in southern California: CI.OLI Olinda; CI.SRN Serrano; CI.MUR Murrieta; CI.LCG La Cienega; CI.RUS Rush; and CI.STC Santa Clara (Figure 1). These strong-motion recording stations are located inside Southern California Edison electrical substations, critical infrastructures that provide essential services to millions of customers. The primary goals of the seismic survey were to understand the potential for amplified ground shaking and to evaluate lateral variability in shear-wave velocity at these sites. We deployed up to 88 geophones at 2-m or 4-m spacing along seven linear profiles surrounding the stations and collocated P- and S-wave sources at ~1-m offset from the geophones. We generated P waves using three types of active sources: a 226-kg vertical accelerated weight-drop (AWD), a 3.5-kg sledgehammer and steel plate combination, and a 2.7-kg hammer and steel plate combination. Active-source S-waves were generated by horizontally striking an aluminum block with a 3.5-kg sledgehammer and by striking a 45-angle aluminum block with a 45°-angle AWD. We first deployed vertical-component geophones (40-Hz, SercelTM L40A, sensitivity of 22.34 volts/meter/second) to record P-wave shots, after which the vertical-component geophones were replaced with horizontal-component geophones (4.5-Hz, SercelTM L28-LBH, sensitivity of 31.3 volts/meter/second) to record S-wave shots. All data were recorded using up to two 60-channel Geometrics Stratavisor NX-60TM seismographs with 24-bit analog-to-digital converters. The seismographs were connected to the geophones via refraction cables. Each shot was recorded at a 0.5-ms sampling rate for two seconds, with data recording starting 100 ms before the actual time of the shot. Ambient noise data were recorded with vertical-component geophones at a 2-ms sampling rate for 120 seconds. This report provides the metadata needed to utilize the seismic data. Acknowledgements: Keith Galvin, Koichi Hayashi, Dan Langermann, Tony Martin, Devin McPhillips, Ian Richardson, David Saucedo-Green, Luther Strayer, Nathan Suits, and Alan Yong Reference: Subcommittee of the SEG Engineering and Groundwater Geophysics Committee, Pullan, S. E., Chairman, 1990, Recommended standard for seismic (/radar) data files in the personal computer environment: Geophysics, vol. 55, no. 9, p. 1260-1271.

This Data Release contains an updated version of the San Andreas catalog of low-frequency earthquakes (LFEs): Shelly, D. R. (2017), A 15 year catalog of more than 1 million low-frequency earthquakes: Tracking tremor and slip along the deep San Andreas Fault, J. Geophys. Res. Solid Earth, 122, 3739–3753, doi:10.1002/2017JB014047. This catalog contains 88 LFE families, with each family consisting of events detected by cross-correlation with the associated waveform template. These templates were identified and located by Shelly and Hardebeck (2010): Shelly, D. R., and J. L. Hardebeck (2010), Precise tremor source locations and amplitude variations along the lower-crustal central San Andreas Fault, Geophys. Res. Lett., 37, L14301, doi:10.1029/2010GL043672. For completeness, we repeat the original catalog information provided in the supplement of Shelly (2017) below, with minor modifications: Catalog Time-Period and Format: The low-frequency earthquake catalog spans from April 2001 to 30 April 2024 and contains 1,528,117 events. Format: YYYY MM DD s_of_day HH mm ss.ss ccsum meancc med_cc seqday ID latitude longitude depth n_chan Explantions: YYYY MM DD (year month day) - Event time (template start time in UTC - ~1s prior to first S-wave arrival time at an HRSN station) s_of_day - Event time (template start time in UTC - ~1s prior to first S-wave arrival time at an HRSN station), second of the day (i.e. 0-86400), HH mm ss.ss (hour, minute, second) - Event time (template start time in UTC- ~1s prior to S-wave arrival time at first HRSN station) ccsum - correlation sum across all stations (must exceed 4.0) meancc - mean correlation among stations with data med_cc - median correlation seqday - sequential day since March 1, 2001 ID - reference ID of family latitude longitude depth - estimated location for that family (Shelly and Hardebeck, 2010) n_chan - number of data channels existing for event (some channels may exist, but not have good data) Family IDs: Each family has an associated identification code, which is a number followed by 1-4 ‘s’. The family IDs are almost meaningless and are simply used as unique identifiers. Originally the numeric code was taken from the second of the day at which the initial template for this family occurred. The number of ‘s’ indicates the number of iterations of stacking and cross-correlation that were applied to derive the template waveforms (see Methods). The lower amplitude and more distant sources typically benefitted from multiple iterations of stacking and cross correlation, before the final template stabilized in its detection set. Data channels Used (station.channels): GHIB.13, EADB.123, JCSB.1, FROB.123, JCNB.123, VCAB.123, MMNB.123, CCRB.123, LCCB.123, SMNB.123, RMNB.123, SCYB.123 JCNB failed in 2008 and was replaced by a shallow sensor. New sensor not used. RMNB failed in 2011 and was not replaced. GHIB.2 was never operational JCSB.23 have poor signal to noise and are not used. VARB was replaced with a new sensor at a new depth in 2003, and this station was not used in original template formation. As of 2024, detection capabilities were substantially degraded with a maximum of 16 channels of data available for detection. This is due to outages in GHIB (since 2020), FROB (since 2023), VCAB (since 2023), and CCRB (since 2022), in addition to the outages described above. It is unclear when/if these stations might be repaired in the future. Channel swap on FROB, VCAB (after BP->SP channel swap, before 2011-7-14): 2011/4/21-2011/7/14: Swap VCAB.2 and VCAB.3 2010/11/10-2011/7/14: Swap FROB.2 and FROB.3 Disregard mean correlation, enforce network correlation sum only (because of poor but present data): 2012/2/13-2014/4/23 Polarity corrections during initial processing: CCRB.123, correct for reversed polarity from 2001-6-1 to 2001-12-13. FROB.123, correct for reverse polarity from 2010/12/10-2011/4/7 MMNB.123, correct for reverse polarity from 2010/12/10-2011/4/7 FROB.23, correct for reverse

In April of 2021, the U.S. Geological Survey conducted a high-resolution seismic survey at Mee Ranch in Monterey County, California. Both passive- and active-source seismic data were acquired using DTCC SmartSolo 3-component nodal seismograph systems ("nodes"), which continuously recorded data at rates up to 2000 samples per second. For passive-source acquisition, a 6x5 grid of nodes was deployed for several weeks before and during the active source shooting. For active-source acquisition, 395 nodes were deployed 1 meter apart (2 meters apart near the endpoints) along a southwest-northeast trend to create an approximately 500-m-long linear array. Additional nodes were deployed at 1 or 2 meter spacing along 25- and 50-m-long linear arrays centered about a known section of the fault. P-wave data were generated near each recording station of the main linear array using a Betsy seisgun firing an 8-gauge blank shotgun shell. P-wave data were also generated every 20 stations along the main linear array using approximately one/third pound of buried explosives. Fault-zone-guided-wave data were generated using explosive sources that were placed within a mapped trace of the San Andreas Fault zone and close to the shorter linear arrays. Finally, S-wave data were generated at each station using an aluminum block struck by a sledgehammer. Shot gathers were created in SEG-Y format (Barry et al, 1975) by extracting several seconds of data from each node for each recorded shot time. The passive grid data were converted to gain-corrected miniseed day files (Ahern and Dost, 2012). This report provides the metadata needed to analyze the seismic data.

This data release contains three netCDF4 files containing grid points of P- and S-wave seismic velocities in Cascadia. This model is an update to Stephenson et al. (2017) Open-File Report 2017-1152, and contains a newly added shallow soil model and optional user-specified topography. A description of the model and its development is provided in the associated Open-File Report. The grid points are given in Universal Transverse Mercator (UTM) Zone 10T, and the grid point depths are given in meters below sea level. The model region extends approximately from 40.2°N to 50°N latitude, and from 121°W to 129°W longitude. The maximum depth of the model region is 59,400 meters. The netCDF4 files range in size from approximately 750 megabytes to 6.2 gigabytes. Water offshore the Pacific Coast is assigned a value of -999 for both the P- and S-wave velocities.