Ramón Verdugo

New Findings on the 1958 Las Melosas Earthquake Sequence, Central Chile: Implications for Seismic Hazard Related to Shallow Crustal Earthquakes in Subduction Zones

On the 4th of September 1958, a sequence of 3 earthquakes of magnitude 6.7–6.9 struck the Andean Main Cordillera at the latitude of Santiago, Central Chile. The quakes were preceded by a magnitude 6.0 foreshock one week earlier. This seismic sequence provided the only documented effects of strong shaking related to shallow earthquakes in a subduction-zone environment in which seismicity is dominated by interplate and intermediate-depth intraplate earthquakes. The 1958 earthquake sequence is reviewed as part of a project of seismic hazard assessment of the densely populated region of Santiago. We reinterpret historical documents and carried out field observations to obtain new intensity estimates, and we estimate ranges of peak acceleration values based on geotechnical back-analyses of earthquake-induced landslides. Estimated peak intensities of 9 and peak accelerations close to 1 g illustrate the significant seismic hazard in areas around active faults in the region and the need to adapt the building codes to these rare but potentially highly destructive types of earthquakes.

Strength and Stiffness of Coarse Granular Soils

A methodology for estimating the shear strength parameters of coarse granular material by means of conventional testing equipment, avoiding the oversized particles and using the finer part of the original soil, is investigated. The procedure uses soil samples with a parallel gradation and a maximum particle size compatible with the available testing facilities. Experimental results obtained for five different coarse granular materials are presented, showing the feasibility of the application of this method.

Seismic Performance of Earth Structures during the February 2010 Maule, Chile, Earthquake: Dams, Levees, Tailings Dams, and Retaining Walls

The 27 February 2010 Maule, Chile, earthquake occurred during the driest time of the year, which implied that most of the soils in the slopes were not saturated and that the dams had extra freeboard. This may explain the small number of slope failures caused by the earthquake. However, two important earth dams suffered seismically induced permanent ground movements, but no catastrophic damage was reported because the reservoirs levels were low. Five medium-sized mine tailings dams failed due to liquefaction; one of them tragically caused four casualties. Retaining structures of all types performed well and no failures were observed.

Effects of Ground Failure on Buildings, Ports, and Industrial Facilities

Soil liquefaction occurred at many sites during the 2010 Maule, Chile, earthquake, often leading to ground failure and lateral spreading. Of particular interest are the effects of liquefaction on built infrastructure. Several buildings were damaged significantly due to foundation movements resulting from liquefaction. Liquefaction-induced ground failure also displaced and distorted waterfront structures, which adversely impacted the operation of some of Chiles key port facilities. Important case histories that document the effects of ground failure on buildings, ports, and industrial facilities are presented in this paper.

Effects of Ground Failure on Bridges, Roads, and Railroads

The long duration and strong velocity content of the motions produced by the 27 February 2010 Maule earthquake resulted in widespread liquefaction and lateral spreading in several urban and other regions of Chile. In particular, critical lifeline structures such as bridges, roadway embankments, and railroads were damaged by ground shaking and ground failure. This paper describes the effects that ground failure had on a number of bridges, roadway embankments, and railroads during this major earthquake.