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8.2.7
Ground Shaking Hazard
Earthquake ground-shaking hazard at the LACDPW Headquarters building is dominated by
faults in close proximity to the site. Most notably, these faults are: (1) the Raymond fault zone,
which has a scarp mapped at the surface approximately 3¾ km (2.4 mile) north of the site and
dips steeply to the north (away from the site); (2) the Verdugo-Eagle Rock fault zone, which is
mapped as having a concealed surface trace approximately 4 km (2½ mile) north- northeast of the
site and dips to the northeast (also away from the site); (3) the Sierra Madre fault zone, which is
mapped as close as approximately 12 km (7½ mile) north- northeast of the site and dips to the
north-northeast (away from the site, as well); and (4) the Hollywood-Santa Monica-Malibu Coast
fault zone, situated about 12 km (7½ mile) to the west. As shown by the hazard curves in Figure
8.8, the Sierra Madre fault is the dominant contributor to short-period (PGA) and 1-second
spectral response at the LACDPW Headquarters site.
Figure 8.8. DPW Building Site Hazard Curves [Geomatrix, 1999]
Geomatrix developed site-specific spectra of Basic Safety Earthquake 1 (BSE-1) and Basic
Safety Earthquake 2 (BSE-2) ground shaking, as defined by FEMA 273. The BSE-1 is the level
of ground shaking that has a 10% probability of being exceeded in a 50- year period. The BSE-2
is the level of ground shaking that has a 2% probability of being exceeded in a 50- year period,
but need not exceed 1.5 times the median deterministic level of ground shaking for maximum
magnitude events on active faults near the site. Due to its very close proximity, Verdugo fault
has potential to produce the strongest ground shaking at the site with a maximum magnitude
M6.9 event (even though the Sierra Madre fault can produce a maximum magnitude M7.2
event). Site-specific response spectra of the BSE-1, the BSE-2 (probabilistic definition) and
maximum magnitude events on the Verdugo and Sierra Madre faults are shown in Figure 8.9.
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