DOE 2000. - Waste Isolation Pilot Plant - U.S. Department of Energy

WIPP RH PSAR DOE/WIPP-03-3174 CHAPTER 2
Up to August 1981, NMT calculated magnitudes differently than other organizations. As a result,
systematic differences in calculated magnitudes were observed. In Table 2.5-3, all magnitudes calculated
by organizations other than NMT were modified by applying corrections. In all cases, these
modifications reduced the reported magnitude by amounts ranging from 0.3 to 0.5.
After August 1981, NMT started using a magnitude scale based on the duration (t D ) of the recorded
signal from onset of the P phase to when the trace amplitude approaches background noise. The equation
used,
M D = 2.79 log t D - 3.63
was derived by LANL researchers 21 and determined to be equivalent to the Richter local magnitude scale
for earthquakes in northern New Mexico. Ake and Sanford 18 established that the LANL formula can be
applied to earthquakes in central New Mexico which fall in the local magnitude range of 1.1 to 4.2. A
careful study of the applicability of the formula to earthquakes in southeastern New Mexico and west
Texas has not been made.
However, random comparisons between magnitudes calculated from the amplitude of S g (Shear Wave)
and duration of ground motion in the time period 1962 to 1974 indicate general consensus good
agreement (within 0.3 magnitude units) between the two methods.
Most recurrence formulas in Section 2.5.4.2 are based on the earthquake data set included in Table 2.5-3,
but at lower magnitudes. Therefore, the latest listing of events within the WIPP facility region does not
require an upward revision in earthquake risk or the DBE.
2.5.1.2.2 Completeness of the Earthquake Data Set
From January 1, 1962 to April 5, 1974, events in the WIPP facility region were located by readings from
stations generally several hundred miles from the epicenter. On April 5, 1974, a single station (CLN)
was established near the center location of the WIPP facility which continued operation to September
1980. These stations are plotted in Figure 2.5-3. From November 1975 to late 1979, a seismograph
array was in operation near Kermit, Texas. These are shown in Figure 2.5-4.
A small network of stations centered in the Davis Mountains of West Texas was operated by the UTA
from July 1977 to July 1978. No stations were running near the location of the WIPP facility from
shutdown of station CLN in September 1980 to startup of a three station network in August 1982. The
WIPP seismograph network was not fully operational until March 1983.
The histograms in Figure 2.5-5 illustrate how the shifts in instrumentation affected the completeness of
the earthquake data set presented in Table 2.5-3. The period from January 1, 1962 through September
30, 1986 was divided into eight time intervals of 1130 days, and the number of events greater than 3.0,
2.5, 2.0, and 1.5 were determined for each interval. The first four intervals (from January 1, 1962
through May 17, 1974) cover the period prior to installation of any stations at, or near the location of the
WIPP facility. The fifth and sixth intervals (from May 18, 1974 through July 24, 1980) cover the period
when station CLN, the Kermit array, and the UTA networks were in operation. Most of the seventh
interval (from July 25, 1980 to August 28, 1983) covers the period between shutdown of station CLN
and startup of the WIPP seismographic network. During the last interval (from August 29, 1983 through
September 30, 1986) the WIPP array was fully operational.
2.5-3 January 24, 2003