The 1987 Whittier Narrows Earthquake in the Los Angeles Metropolitan Area, California

Abstract

The Whittier Narrows earthquake sequence (local magnitude, M(L) = 5.9), which caused over $358-million damage, indicates that assessments of earthquake hazards in the Los Angeles metropolitan area may be underestimated. The sequence ruptured a previously unidentified thrust fault that may be part of a large system of thrust faults that extends across the entire east-west length of the northern margin of the Los Angeles basin. Peak horizontal accelerations from the main shock, which were measured at ground level and in structures, were as high as 0.6g (where g is the acceleration of gravity at sea level) within 50 kilometers of the epicenter. The distribution of the modified Mercalli intensity VII reflects a broad north-south elongated zone of damage that is approximately centered on the main shock epicenter.

Evidence for Vertical Partitioning of Strike-Slip and Compressional Tectonics from Seismicity, Focal Mechanisms, and Stress Drops in the East Los Angeles Basin Area, California

“…This could be caused by different velocity models or different sets of phase picks being used in the two different approaches. We prefer the deeper depths because they are more consistent with previous studies (Hauksson et al, 1988(Hauksson et al, , 2008.…”

“…In the ELA basin, the Whittier fault is the longest mapped fault, with a surface trace along the whole length (around 40 km), striking to the northwest. Over the past 30 years, two moderate-size earthquakes occurred inside the ELA basin close to the Whittier fault: the 1 October 1987 Whittier Narrows M L 5.9 and the 29 July 2008 Chino Hills M w 5.4 earthquakes (e.g., Hauksson et al, 1988Hauksson et al, , 2008Hauksson and Jones, 1989). The focal mechanisms exhibited reverse faulting for the Whittier Narrows mainshock and oblique faulting for the Chino Hills mainshock.…”

Low‐angle normal faults and seismicity: A review

“…Active low-angle normal faults may be difficult to detect on the basis of surface rupture patterns and paleoseismicity (e.g., the Sevier Desert detachment), as are low-angle thrust faults [e.g., Hauksson et al, 1987] …”

Earthquakes, faulting, and stress in the Los Angeles Basin

“…In ]. This complexity has made it difficult to interpret the ongoing tectonic deformation and the associated earthquake activity, which, in turn, has resulted in "surprise" earthquakes causing significant property damage [e.g., Hauksson et al, 1988]. This study has contributed toward understanding the complex tectonics through mapping of fold and thrust belts using geologic data and earthquake focal mechanisms and suggesting that the coexistence of strike-slip and thrust faults is the result of alecoupling of oblique fault motion.…”