Comparison of 1989 Loma Prieta earthquake damage to mapped lineaments along the range front of the Santa Cruz Mountains, California

Abstract

Damage to public infrastructure at or below the ground surface (streets, curbs, and water and gas lines) in southwestern Santa Clara Valley, California, associated with the 1989 Loma Prieta earthquake, is used to support the assertion that the series of photointerpreted lineaments are tectonic in origin and related to long-term reverse faulting along the range front of the Santa Cruz Mountains. We quantitatively analyze whether the photointerpreted lineaments are spatially correlated with earthquakeinduced damage by examining whether the damage was located preferentially closer to the mapped lineaments than to a spatially random set of points. The analysis confi rms that damage related to the Loma Prieta earthquake is located preferentially close to mapped lineaments. This result supports the assertion that the lineaments have a tectonic origin related to range-front faulting along the Santa Cruz Mountains, and that their presence may be related to primary fault rupture, spatially focused shaking damage, or slip triggered by strong motion induced by nearby faults.

Deformation from the 1989 Loma Prieta earthquake near the southwest margin of the Santa Clara Valley, California

“…Their experiments, however, indicate that ground shaking intensifi ed by this mechanism should generally occur in bands concentric to the hypocenter. This orientation is roughly normal to the zones of damage shown in Figures 1 and 6 (Phelps et al, 2015), suggesting that this mechanism was not the dominant control on the damage zones.…”

“…Individual breaks typically were not prominent enough to provide measurable displacements, and local alignment of breaks was detectable in only a few places. Consequently, the spatial distribution of this damage provided the principal evidence of its origin (see Phelps et al, 2015). We assembled information on damage by mapping its occurrence in the fi eld and by compiling reports of damage from utility companies and public agencies.…”

“…The times of damage generation are not known in detail, and so some of the damage may actually have occurred in response to foreshocks or aftershocks. The principal limitation is the spatial distribution of concrete and pipes that is largely limited to the semiregular network of straight streets in fl atland areas (see Phelps et al, 2015). Therefore, a lack of mapped damage may simply refl ect a lack of concrete and pipes rather than absence of ground deformation.…”

“…Damage at 30% of the sites was indicative of shortening. Spatially, the sites are clustered; 54% are within the Los Gatos USGS 7.5 min quadrangle (Phelps et al, 2015).…”

Basement Fault Reactivation in the Zakho– Silopi Region, Iraqi Kurdistan – Turkey Border

“…The alignment of earthquake epicentres clearly indicates that there is a subsurface seismically active basement fault and could be the source of strong earthquakes in the future (Jacobi, 2002;Almeida-Filho et al, 2009;Talukdar and Barman, 2012;Saravanavel and Ramasamy, 2014;Phelps et al, 2015). Some of the seismic lineaments were interpreted along the southeastern region of the United States based on epicentral alignments of earthquakes (Nowroozi, 1995).…”