Catalog Details

Utah Region

Yellowstone Region


Format for Earthquake Summary Data July 1962 – Present

Column Format Description
1-2 I2 Year
3-6 I4 Date in Universal Coordinated Time (UTC)
8-11 I4 Origin time hour and minute, UTC
13-17 F5.2 Origin time seconds
19-20 I2 Latitude north, degrees
22-26 F5.2 Latitude minutes
28-30 I3 Longitude west, degrees
32-36 F5.2 Longitude minutes
39-43 F5.2 Depth in km below datum, which is sea level for earthquakes from Oct. 1, 2012, to the present. For earlier earthquakes, the datum is 1.5 km above sea level for the Utah region and 2.0 km above sea level for the Yellowstone region.
44 A1 “*” for fixed or poor quality depth
45 A1 “W” if the magnitude is a local magnitude (ML), calculated from peak amplitudes on Wood-Anderson records; otherwise it is a coda magnitude (MC), calculated from signal durations. For pre-1981 events, some “W” magnitudes are averages of MLs and MCs.
46-50 F5.2 Magnitude (-9.99 if unavailable)
52-53 I2 NO, the number of P and S arrival times used in the location
55-57 I3 GAP, the maximum azimuthal separation between recording stations used in the location, degrees
58-62 F5.1 DMN, the horizontal distance from the epicenter to the nearest station used in the location, km
63-67 F5.2 RMS, the weighted root-mean-square of the differences between the observed and calculated arrival times, sec
68-72 F5.1 ERH, the horizontal standard error, km
73-77 F5.1 ERZ, the vertical standard error, km
79 A1 Q, location quality (if computed)


Utah Region Earthquake Catalog

The Utah region earthquake catalog is a list of documented earthquakes that have occurred in the Utah region since 1850. The Utah region is defined as the area extending from 36º 45´ – 42º 30´ North latitude and from 108º 45´ – 114º 15´ West longitude. This region includes the State of Utah and areas of neighboring states within approximately 30´ of the northern border of Utah and 15´ of the eastern, western, and southern borders.

2006 Revision of the 1981-2001 Catalog

In 2006, the University of Utah Seismograph Stations (UUSS) completed a major revision of the magnitudes in the 1981-2001 Utah region catalog. This revision added nearly 900 magnitude determinations of the preferred type (local magnitude, ML) for the time period 1994-2001. It also corrected systematic, time-dependent errors of up to 0.4 units in the other, more common type of magnitude determination (coda magnitude, MC) used during 1981-2001. Finally, stricter standards for data quality and type were adhered to in computing the revised magnitudes. See Summary of UUSS Magnitude Determinations: 1981-2006 for a more complete description of the magnitude revisions. When the magnitude changes were implemented, miscellaneous other problems in the catalog were also corrected.

Data

The UUSS instrumental earthquake catalog for the Utah region begins in July 1962. The July 1, 1962, to September 30, 1974, catalog is based on instrumental earthquake locations from a skeletal regional seismic network (less than 10 stations statewide before 1974). Beginning in October 1974, data are available from a denser network of high-gain telemetered stations, enabling significantly better locations and magnitude determinations than for the previous time period. The size of the network in and within 100 km of the Utah region expanded from 26 stations in late 1974 to 55 stations by the end of 1980 and 72 stations by the end of 1996 (including stations operated by other agencies and recorded by UUSS). UUSS began adding broadband digital telemetry stations to the network in 1997 and digitally telemetered strong motion stations in 2000. As of January 2006, UUSS was recording data from 175 stations in and within 100 km of the Utah region: 90 high-gain and 85 strong-motion.

From 1962 to 1973, data from most seismograph stations in the Utah region were recorded on site using photographic paper drum recorders. From 1974 though 1980, the network data were recorded primarily on 16 mm analog film recorders (Develocorders) located at the University of Utah. Beginning in January 1981, the network data were recorded digitally on a DEC PDP-11/34 computer system at the University. Digital recording was switched from the PDP-11/34 computer to a Concurrent 7200 computer on September 17, 1992. Additional recording systems for the digital telemetry data were added beginning in 1997. Descriptions of earthquake recording and seismicity in the Utah region can be found in Arabasz et al. (1979, 1980, 1992) and Smith and Arabasz (1991).

Data Processing and Analysis, 1981-present

Data processing and analysis procedures for the pre-1981 Utah region earthquake catalog are documented in Arabasz et al. (1979, 1980) and Richins et al. (1980). The procedures for the 1981-present catalog are described in Nava et al. (1990) and other published catalogs referenced therein, and in the following more up-to-date documents:

References

Arabasz, W. J., R. B. Smith, and W. D. Richins, Editors (1979). Earthquake Studies in Utah, 1850 to 1978, Special Publication, University of Utah Seismograph Stations, Salt Lake City, Utah, 552 pp.

Arabasz, W. J., R. B. Smith, and W. D. Richins (1980). Earthquake studies along the Wasatch Front, Utah: Network monitoring, seismicity, and seismic hazards, Bull. Seism. Soc. Am. 70, 1479-1499.

Arabasz, W.J., J.C. Pechmann, and E.D. Brown (1992). Observational seismology and the evaluation of earthquake hazards and risk in the Wasatch front area, Utah, in Assessment of Regional Earthquake Hazards and Risk Along the Wasatch Front, Utah, P.L. Gori and W.W. Hays (Editors), U.S. Geol. Surv. Profess. Paper 1500 A J, D1 D36.

Nava, S. J., J. C. Pechmann, W. J. Arabasz, E. D. Brown, L. L. Hall, P. J. Oehmich, E. McPherson, and J. K. Whipp (1990). Earthquake Catalog for the Utah Region, January 1, 1986 to December 31, 1988, Special Publication, University of Utah Seismograph Stations, Salt Lake City, Utah, 96 pp.

Richins, W. D., W. J. Arabasz, G. M. Hathaway, P. J. Oehmich, L. L. Sells, and G. Zandt (1981). Earthquake Data for the Utah Region, July 1, 1978 to December 31, 1980, Special Publication, University of Utah Seismograph Stations, Salt Lake City, Utah, 127 pp.

Smith, R. B., and W. J. Arabasz (1991). Seismicity of the Intermountain Seismic Belt, in Neotectonics of North America, D.B. Slemmons, E.R. Engdahl, M.D. Zoback, and D.D. Blackwell (Editors), Geol. Soc. Am. Decade Map Vol. 1, 185-228.


Yellowstone Region Earthquake Catalog

The Yellowstone region earthquake catalog is a list of instrumentally located earthquakes that have occurred in the Yellowstone region since November 1972. The Yellowstone region is defined as the area extending from 44º 0´ – 45º 10´ N latitude and from 109º 45´ – 111º 30´ West longitude. This region includes Yellowstone National Park and neighboring areas within approximately 24´ of the western park boundary, 15´ of the eastern park boundary, and 8´ of the northern and southern park boundaries. The U.S. Geological Survey (USGS) produced the original version of the catalog for the time period 1973-1981 (Pitt, 1987). The University of Utah Seismograph Stations (UUSS) produced the catalog for 1982 to the present (see Nava et al., 1996, and references therein).

2006 Revision of the 1982-2001 Catalog

In 2006, the UUSS completed a major revision of the magnitudes in the 1982-2001 Yellowstone region catalog. This revision added more than 400 magnitude determinations of the preferred type (local magnitude, ML) for the time period 1994-2001. It also corrected a systematic magnitude overestimation averaging 0.9 units in the other, more common type of magnitude determination (coda magnitude, MC) used during 1982-2001. See Summary of UUSS Magnitude Determinations: 1981-2006 for a more complete description of the magnitude revisions. Miscellaneous other problems in the catalog were corrected at the same time that the magnitude changes were implemented.

Husen and Smith (2004) produced a catalog of Yellowstone earthquakes for the time period November 1972 through December 2002 that features hypocenters computed using a three-dimensional velocity model. Their hypocenters should be more accurate than those in the UUSS catalog, which were computed using a one-dimensional velocity model (see Computation of UUSS Earthquake Locations: 1981 – Present ). However, the magnitudes in the UUSS catalog are an improvement on those in the Husen and Smith (2004) catalog. The UUSS catalog includes MLs for some earthquakes, whereas the Husen and Smith catalog does not. The MCs in the Husen and Smith catalog are mostly the same as in the UUSS catalog because they used the same methodology to compute them. However, Husen and Smith (2004) discarded as unreliable all MCs based on data from less than three stations. To avoid discarding these magnitudes, UUSS put considerable effort into adding data from more stations to these questionable MC determinations and performing various checks on all of the revised coda magnitudes (see Summary of UUSS Magnitude Determinations: 1981-2006 ).

The old Yellowstone catalog for 1981-2001 has about 18% more earthquakes than both the Husen and Smith (2004) catalog and the new UUSS catalog. The difference is primarily due to the fact that the old catalog included some earthquakes located with arrival time picks that came entirely from an automatic picking program or from seismic networks outside of the Yellowstone region (e.g., Nava et al., 1993).

Data

The Yellowstone earthquake catalog is based primarily on data from a telemetered seismic network in the Yellowstone region. The U.S. Geological Survey operated this network from 1972 through 1981 and from 1984 until 1991 (Pitt, 1987). Until 1981, the data from this network were recorded at Yellowstone Park Headquarters at Mammoth, Wyoming (on tape recorders) and at the USGS office in Menlo Park, California (primarily on 16-mm analog film recorders), and were analyzed by the USGS. The Yellowstone network did not operate during 1982 and 1983. The locations and magnitudes for the few earthquakes in the catalog during this two-year period were determined by UUSS using data from other seismic stations in the vicinity. In November 1983, digital computer recording and analysis of the Yellowstone network data was initiated at the UUSS through the support of the USGS and the National Park Service. Operation and maintenance of the network was transferred to the UUSS in 1991.

The number of stations in the Yellowstone seismic network varied considerably from 1972 through 1981, reaching a high of 26 stations in October 1974 (Husen and Smith, 2004). From 1984 through 1991, the network consisted of 16 vertical-component stations. Three-component stations were added beginning in 1993 and broadband digital telemetry stations beginning in 1995. As of September 2006, the network consisted of 26 stations: six broadband 3-component digital telemetry stations—including two maintained by the USGS, three 3-component short-period stations, and 17 vertical-component short-period stations. Descriptions of the general seismicity and history of seismic recording in the Yellowstone National Park region can be found in Smith and Arabasz (1991) and Husen and Smith (2004).

Data Processing and Analysis, 1981-present

The data processing and analysis procedures for the 1982-present catalog are described in Nava et al. (1996) and other published catalogs referenced therein, and in the following more up-to-date documents:

References

Husen, S., and R. B. Smith (2004). Probabilistic earthquake relocation in three-dimensional velocity models for the Yellowstone National Park region, Wyoming, Bull. Seism. Soc. Am. 94, 880-896.

Nava, S. J., R. B. Smith, L. L. Hall, E. McPherson, P. J. Oehmich, and R. A. Hutchinson (1993). Earthquake Catalog for the Yellowstone National Park Region: January 1 to December 31, 1991, Special Publication, University of Utah Seismograph Stations, Salt Lake City, Utah, 29 pp.

Nava, S. J., R. B. Smith, L. L. Hall, J. K. Whipp, E. McPherson, and R. A. Hutchinson (1996). Earthquake Catalog for the Yellowstone National Park Region: January 1, 1992 to December 31, 1994, Special Publication, University of Utah Seismograph Stations, Salt Lake City, Utah, 61 pp.

Pitt, A.M. (1987). Catalog of earthquakes in the Yellowstone National Park – Hebgen Lake Region, Wyoming, Montana, and Idaho, for the years 1973 to 1981, U.S. Geol. Surv., Open-File Rept. 87-611, 65 pp.

Smith, R. B., and W. J. Arabasz (1991). Seismicity of the Intermountain Seismic Belt, in Neotectonics of North America, D.B. Slemmons, E.R. Engdahl, M.D. Zoback, and D.D. Blackwell (Editors), Geol. Soc. Am. Decade Map Vol. 1, 185-228.