Appendix B - Appendix Earthquake Catalog Database
This appendix contains descriptions of the earthquake catalog database assembled for the CEUS-SSC Project. The earthquake catalog is described in Chapter 3 of the report; the database components are discussed in the following sections.
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B.1 CEUS-SSC Uniform Moment Magnitude Earthquake Catalog
The primary product of the earthquake catalog development described in Chapter 3 is a catalog of earthquakes for the CEUS in which earthquake size is reported as moment magnitude, M, as defined by Hanks and Kanamori (1979). The catalog forms the basis for the assessment of the earthquake recurrence rates for the distributed seismic sources, and it is used in the assessment of Mmax for those sources. The magnitudes are reported as E[M], the expected moment magnitude given the uncertainty in its assessment. The development of the concept of E[M] and its derivation from the observed size measures are described in Section 3.3.1. Also explained in Section 3.3.1 is the assessment of the equivalent count values N* used to obtain unbiased earthquake recurrence parameters.
Table B-1 lists the CEUS-SSC Project uniform moment magnitude catalog. The explanation of the fields in the table is given below.
| TID | Unique identification number assigned in the project to each earthquake. These values are not necessarily sequential. Sequential numbering of earthquakes in the uniform magnitude catalog is provided by the EQNO field. |
| Year, Month, Day | Earthquake Date |
| Hour, Minute, Second | Earthquake Time. The times are assumed to be expressed in Coordinated Universal Time (UTC). During assembly of the catalog, UTC was selected when it was clear that various other time zone standards were used in the catalog sources. However, the reported times are based primarily on those reported in the source catalogs, and no attempt was made to verify that the time was UTC for the individual sources. The master catalog database contains all of the individual catalog entries with their individual times. |
| Latitude, Longitude | Earthquake Location (degrees). The precision of the reported location represents the precision reported for the preferred entry among the source catalogs. Variability in the precision in location among the earthquake entries is not an issue, as the earthquake recurrence rates are computed using grid sizes of 1/4 or 1/2 degree longitude and latitude. |
| Depth | Earthquake Depth (km) |
| ERH | Estimated Horizontal Location Uncertainty (km). This entry provides a measure of the uncertainty in location of the earthquake. The values represent a mixture of reported standard errors in location of instrumentally located earthquakes from various catalog sources and estimates of location uncertainty for locations based on felt effects (shaking intensity). |
| E[M] | Expected value of moment magnitude. |
| N* | Equivalent earthquake count. This value is used to account for the effects of magnitude uncertainty in computing unbiased earthquake recurrence parameters. |
| sigM | Standard error in the estimated moment magnitude, E[M]. It is used to compute N*. |
| EQNO | Earthquake number in the uniform moment magnitude CEUS-SSC Project catalog. |
| Flag | Flag for dependent earthquakes. A value of 0 indicates an independent earthquake, and a value greater than 0 indicates a dependent earthquake. For dependent earthquakes the value of FLAG is the EQNO of the main shock of the cluster. |
The primary method for the development of the uniform moment magnitude measure was the use of conversion relationships developed by regression of reported moment magnitudes against other size measures for individual earthquakes. Table B-2 provides a list of the moment magnitude values obtained from the literature for earthquakes in the CEUS-SSC Project database. The table gives the date, time, and location of an earthquake and the reported value of moment magnitude, Mˆ . The M with a hat symbol denotes moment magnitude measured with uncertainty (see Section 3.3.1 for a discussion). The table also lists the source of the reported values. Multiple entries for individual earthquakes were factored into the overall uncertainty in the assessment of the moment magnitude and into the uncertainty in the assessment of moment magnitude from the conversion relationships.
B.3 Approximate Moment Magnitude Data
As discussed in Section 3.3.2.2, studies by Atkinson (2003), Boatwright (1994), and Moulis (2002) provide approximate estimates of moment magnitude. Listed in Table B-3 are the moment magnitude values reported by these authors for earthquakes in the CEUS-SSC Project catalog. For each author, the data include (1) the magnitude reported by the author, (2) the value of estimated moment magnitude, E[M], and (3) the standard error (denoted sigma M) in the E[M] obtained using the conversion relationships shown on Figures 3.3-2, 3.3-3, and 3.3-4. Also listed in the table is the composite value of E[M] and its standard error sigM obtained from combining the individual estimates using Equations 3.3.1-9 and 3.3.1-10.
The composite listing of the earthquake catalog data gathered for CEUS-SSC Project is contained in the master catalog data file CEUS_SSC_Earthquake_Catalog_Data_Rev7.xls located on the project website (www.ceus-ssc.com). The file contains all the entries from the individual catalog sources assembled to produce the earthquake catalog for the project. The master catalog data file also contains those entries that are identified as nontectonic events (e.g., nontectonic mechanisms such as explosions and false entries in the source catalogs) and entries for earthquakes with magnitudes smaller than those of interest for use in assessing earthquake recurrence rates for the CEUS-SSC Project.
The primary purpose of including the master catalog database is to provide a basis for comparing the CEUS-SSC Project catalog with additional information that may become available about the earthquakes included in the catalog and comparing catalog entries from other sources with the entries in the database.
The fields contained in the master catalog data file are described below.
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