Routine United States Mining Seismicity

Explanation of Catalog Listings

Most hypocenters and magnitudes in "Routine Mining Seismicity in the United States" catalogs are computed by the algorithms used by the USGS/NEIC to compute source parameters of earthquakes. More detailed explanations of the source parameters may be found in the January and July issues of the publication, "Preliminary Determination of Epicenters, Monthly Listing", published by the USGS/NEIC.

Abbreviations in Heading

MB
Body wave magnitude computed by the USGS/NEIC. Because USGS/NEIC practice is to calculate MB using P-wave amplitude data from stations more than 15 degrees from the epicenter, very few of the routine mining seismic events are sufficiently large that MB can be computed.
Msz
Vertical surface wave magnitude. To date, none of the routine mining seismic events have been large enough, or rich enough in long-period energy, that Msz could be computed for them.
UTC
Coordinated Universal Time. HR MN SEC - Hour, minute, second
SD
Standard Deviation from the arithmetic mean of primary phase, P-wave/PKP-wave, residuals
No. Sta.
Number of stations reporting P or PKP phases used in computation. Stations used in "Routine Mining Seismicity in the United States" are only those for which digital traces are recorded at the USGS/NEIC.

Symbols Following Origin Time

The following symbols indicate the precision of the solution, as indicated by the 90% confidence ellipse on the epicentral coordinates. The orientation and semi-axes lengths of the confidence ellipses are given in the bulletins (mchedrYYMMex.dat) and catalog (mineevents.gct) that are available by anonymous ftp (ftp://hazards.cr.usgs.gov/mineblast/). The confidence ellipses are estimated under the assumption that travel-time tables used to locate the seismic events (1940 Jeffreys-Bullen P and 1968 Bolt PKP travel-time tables) are appropriate for the event-to-station path and under the assumption that errors in arrival-time readings are Gaussian. Because neither of the above assumptions is likely satisfied, the 90% confidence ellipses for most epicenters probably underestimate the uncertainty of those epicenters.

?
Indicates a poor solution, published to make the catalog more complete. In general, the geometric mean of the semi-major and semi-minor axes of the epicenter's 90% confidence ellipse is greater than 16.0 km.
*
Indicates a less reliable solution. In general, the geometric mean of the semi-major and semi-minor axes of the epicenter's 90% confidence ellipse is greater than 8.5 km and less than or equal to 16.0 km.

The lack of any symbol indicates that the geometric mean of the semi-major and semi-minor axes of the epicenter's 90% confidence ellipse is less than or equal to 8.5 km.

Symbols Following Depth

G
indicates that depth was restrained by a geophysicist. Most mining associated events are restrained to a 0 km depth.

Items under "REGION, CONTRIBUTED MAGNITUDES, AND COMMENTS"

Broad geographic regions- The broad geographic regions given in upper case letters in the "REGION, CONTRIBUTED MAGNITUDES, AND COMMENTS" column are determined from a representation of political boundaries that is defined at one degree intervals (Flinn and others, 1974). This representation accounts only approximately for many state boundaries, and, for this reason, some epicenters are attributed to states that are adjacent to the states in which the epicenters are actually located.

ML (GS)
Local magnitude computed according to the formula of Richter (1935). There are two major differences between the ML given in the present catalog and those that would be computed by strict application of Richter's formula. First, the ML quoted in "Routine Mining Seismicity in the United States" are based on amplitudes picked from traces of vertical-component, electronically amplifying, seismographs, whereas Richter's formula was defined for amplitudes picked from the traces of horizontal-component, optically amplifying, seismographs. Second, the ML quoted in "Routine Mining Seismicity in the United States" are computed for seismic events from throughout the western United States, whereas Richter's formula was defined for Southern California, and implicitly incorporates the attenuative properties of Southern California crust and mantle.
mbLg (GS)
Magnitude calculated from amplitudes of Lg phases at an approximately 1-second period, according to the formulas of Nuttli (1973), who defined mblg so that mbLg and mb from the same seismic event would be approximately equal. In "Routine Mining Seismicity in the United States", mbLg (GS) are computed principally for seismic events in the central and eastern Unitied States.

Specific geographic location - Specific geographic locations of mining-associated seismic events are given with respect to nearby town names. Mining Seismicity Source Regions summarizes characteristics of locations from which many mining-associated seismic events have been cataloged.

References