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(Ms) between magnitude 5.5 to 8.0 and local magnitude (ML) below magnitude 6.0
(Kanamori, 1983). '

The peak ground acceleration (PGA) at the‘ project property associated with the MCE and
MPE for each source fault is estimated using the composite attenuation relationships of

Joyner and Boore (1988) and Donovan and Becker (1986) as updated by Dames & Moore’s
Dr. Neville C. Donovan. This relationship is the arithmetic mean of five commonly used,
published and unpublished attenuation relationships. The source distance (Table 7) used
for the Donovan and Becker (1986) relationship is the closest distance between the mapped
or inferred surface trace of the source fault and the project property, except in the case

where a fault has a significant dip toward the property. In these cases (e.g., San
Fernando-Sierra Madre fault zone), the projection of an 8 km hypocentral depth along the
fault plane to the ground surface was used to estimate a source distance. For the Joyner
and Boore (1988) relationship, the source distance was calculated as outlined in their
methodology.

Based on estimated fault capability and proximity, a MCE on the San Fernando-Sierra
Madre fault zone would most likely generate the strongest ground accelerations at the
project property. As shown in Table 7, estimated mean PGA of 0.54 to 0.60g (gravity) may
be associated with this event. A MCE on the San Gabriel fault or the Santa Susana fault
zone is expected to result in slightly lower levels of shaking of about 0.50 to 0.51g and

0.45 to 0.46g, respectively. Based on the results of the analysis of MPE’s, a postulated MPE
of Mw 6 1/2 on the San Fernando-Sierra Madre fault zone would likely generate the highest
PGA at the site of 0.41 to 0.52g. These estimated ground motion values are intended for
environmental review purposes only. Design-basis estimates of PGA at the project property
will need to be developed during engineering design.

The theoretical PGA at the project property calculated for a MPE on San Fernando-Sierra
Madre fault zone (approximately 0.45g) is comparable to measured accelerations recorded
at a number of stations in the project region during the 1971 Mw 6.6 San Fernando
earthquake. Several accelerograph stations were located on the upper thrust plate, including

stations Pacoirna Darn, Lake Hughes (Station No. 12), and Castaic Dam, located
approximately 5 miles, 12 miles, and 14 miles from the project property, respectively (Cloud
and Hudson, in Oakeshott, 1975). About 15 to 18 miles from the epicenter, PGA’s of 037g
and 0.39g were recorded at Lake Hughes and Castaic Dam, respectively. The highest ever

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