Source- and Site-effects in the Intensities of the M 5.4 29 July 2008 Earthquake in South Los Angeles

Abstract

This paper discusses the source- and site-effects on the distribution of macroseismic intensity, estimated or observed, following the 29 July 2008 M 5.4 earthquake in the greater Los Angeles metropolitan region. We refer to the instrumental intensities according to the ShakeMap procedure (Wald et al. 2006) and the U.S. Geological Survey (USGS) Community Internet Intensity Map (CIIM; Atkinson and Wald 2007). The CIIMs are also known as the “Did You Feel It?” questionnaires (DYFI). Both ShakeMap and CIIM are openly available through the USGS Web site (http://earthquake.usgs.gov/eqcenter). Note that the traditional modified Mercalli intensities (MMI; Wood and Neumann 1931) from the so called felt reports are not available for the study earthquake. Three original techniques designed to address intensities are used here: 1) a simple kinematic formula for S -body-waves, KF (Sirovich 1996, 1997); 2) a “parametric KF scenario” (Sirovich and Pettenati 2004b, 2009; Pettenati and Sirovich 2006; Pettenati et al. 2008); and 3) the isoseismals obtained through natural neighbor interpolation (Sirovich et al. 2002; and see below. We also test our KF parametric technique for hazard planning and its chance of improving fast information after moderate earthquakes (mostly in regions with insufficient instrumental coverage, where an isotropic, predictive, empirical equation is not satisfactory). Intensities are treated here as integer values for two reasons: first, to adhere to the original definition of MMI by Wood and Neumann (1931), and second, because our strategic target is the treatment of the remarkable database of high-quality traditional macroseismic observations, obtained by seismologists and historians, which is available in Europe going back at least to the XVI–XVII centuries (see, for example, the Italian intensity data in Stucchi et al. 2007). Figure 1 shows the ShakeMap instrumental intensities near the meizoseismal area, modified to indicate integer values rather than …