Following the 23 October 2004 Niigata Ken Chuetsu, Japan, Mw 6.6 earthquake, LIDAR (light detection and ranging) technology was used to create ultra high-resolution three-dimensional digital terrain models of the earthquake damage. Two reconnaissance teams traveled with tripod-mounted LIDAR that allowed for the rapid collection of post-earthquake failure geometries of ground, structures, and lifelines prior to modification by post-disaster recovery efforts and natural processes, with range accuracies of approximately 2.5 cm and targets illuminated up to 400–700 m from the sensor. LIDAR offers several benefits: (1) detailed failure morphologies of damaged ground and structures, measured remotely and in a way not feasible by conventional means; (2) exploration and visualization of damage on a computer screen is enabled, in orientations and scales that were previously impossible, providing better definition of the failure surfaces, deformation patterns, and morphologies required for understanding failure modes; and (3) archived ultra-high-resolution data for evaluation of analytical and numerical models of deformation. High-resolution images and movies of LIDAR data can be viewed at http://walrus.wr.usgs.gov/geotech/Niigata/ and the online pages of Earthquake Spectra.

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The Mw 8.4 23 June 2001 Southern Peru earthquake generated intense ground motions in a large region encompassing southern Peru and northern Chile. The earthquake was recorded by seven strong motion stations with peak ground accelerations ranging from 0.04 g to 0.34 g for site-to-fault distances ranging from about 70 km to 220 km. At this time, there are no other strong motion records for an earthquake of this magnitude. Hence, the strong motion data set from this earthquake is unique and of particular interest to engineers dealing with seismic design in subduction regions. This paper presents an engineering analysis of the strong motion records. Shear-wave velocity profiles were measured using Spectral Analysis of Surface Waves methods at four stations. Measured shear-wave velocities are high, indicating that all sites classify as stiff soil sites (Site C) according to the International Building Code classification scheme. The strong motion set is characterized by strong high frequency content at large distances from the fault. Site response contributed at least in part to the observed high frequency content in the ground motions. In general, current attenuation relationships for spectral acceleration underpredicted the observed ground motions.

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