The Pisco, Peru, Earthquake of August 15, 2007
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EERI Special Earthquake Report — October 2007 Learning from Earthquakes The Pisco, Peru, Earthquake of August 15, 2007 EERI team leader Eduardo A. Fierro Crete, and Erick Ortega and Pablo ple were killed and ,090 were in- of BFP Engineers, Inc. (Bertero, Broncano of Direccion de Hidrografia jured. The majority of the damage Fierro, Perry), in Berkeley, Califor- y Navegacion of the Peruvian Navy. and casualties occurred in Chincha nia, visited the area affected by the Alta, Ica, and Pisco (Figure ). Most The teams visited the following cities: earthquake August 18-24, 2007. of the buildings destroyed were Pisco, Chincha, Canete, Ica, San Professor Marcial Blondet of the adobe housing. Hospitals, schools, Andres, Tambo de Mora and Lima. Pontificia Universidad Católica del and other medium-to-large public All cities were within 97 km of the Perú (PUCP) in Lima participated buildings were also damaged. Most epicenter, with the exception of Lima, as an in-country member of the of these buildings are built using located about 145 km away. The EERI team, providing critical assis- reinforced concrete frames and infill EERI team joined up with the PUCP tance in the field. Other members brick masonry rigidly attached to team led by Nicola Tarque, who start- of the EERI team included Donald the frames. ed the site inspection on August 17. Ballantyne of ABS Consulting, Inc., The PUCP team included Luis Carlos Widespread communications and in Tacoma, Washington; Mikael Fernandez and Jesus Carpio from power outages occurred in the Gartner of Nabih Youssef & Asso- PUCP, and Eric Hulburd from Stan- area. The Pan American Highway, ciates in Los Angeles, California; ford University. the Carretera Central, and other Adolfo Matamoros of the University main transport routes suffered of Kansas; Kim Shoaf and Alina The EERI team and the publication of heavy damage due to landslides Dorian of the Center for Public this Learning from Earthquakes re- and liquefaction. A small tsunami Health and Disasters at the Uni- port were supported by the National resulted in wave heights of 00 cm versity of California at Los Ange- Science Foundation through grant at Callao and La Punta, Peru; 36 les; and Hope Seligson of MMI #CMII-0131895. NSF supported the cm at Arica, 28 cm at Coquimbo, Engineering in Huntington Beach, GEER team and the tsunami survey and 7 cm at Valparaiso, Chile. California. EERI collaborated with team through grants #CMII-0323914 and CMS-0646278, respectively. many other investigators in the Seismological Aspects field, including Liliana Pinto and Kent Yu of Degenkolb Engineers, Introduction The Pisco earthquake was the re- Mario Rodriguez of UNAM, San- sult of the subduction process be- The Mw 8.0 Pisco earthquake struck tiago Pujol of Purdue University, tween the Nazca plate and the at 6:40 p.m. local time. The epicenter and Arturo Schultz of the University South American continental plate. was about 45 km west-northwest of of Minnesota, representing The This subduction process results in Chincha Alta, or about 45 km south- Masonry Institute. a high rate of seismicity along the southeast of Lima. At least 59 peo- Adrian Rodriguez-Marek of Wash- ington State University led the Geo- Figure 1. Engineering Earthquake Recon- Overview naissance (GEER) team and also map and served as a member of the EERI Paracas team. His team included Brady Cox peninsula of the University of Arkansas; detail map Jorge Meneses of Kleinfelder, Inc., showing in San Diego, California; Viviana reconnais- Moreno and Manuel Olcese of sance track PUCP; Rodolfo Sancio of Golder with tsunami Associates in Houston, Texas; and survey loca- Joseph Wartman of Drexel Univer- tions, gener- sity in Philadelphia, Pennsylvania. alized runup A tsunami reconnaissance team heights, and was composed of Hermann Fritz earthquake (team leader) of the Georgia In- location. stitute of Technology, Nikos Kalli- geris of the Technical University of (Background satellite imagery: Europa Technologies/Google Earth) EERI Special Earthquake Report — October 2007 Figure 2. East-west spectral accelerations recorded by CISMID stations (from Lazares et al., 2007). All stations are located at a range of 96-111 km from the fault plane. The Rimac and San Figure 3. Acceleration, velocity, and displacement Isidro stations are located on dense, stiff gravel deposits (re- time histories for the La Molina record (stiff soil). ferred to as Lima Conglomerate); the La Molina station is lo- cated on shallow soil overlying the denser Lima Conglomerate; ground surface projection of the the Callao station is located on soft soil. fault plane. The earthquake was recorded at 6 coasts of Peru and Chile. The earth- had a moment magnitude (Mw) of 8.0 stations within 50 km of the fault quake was an interface event and (USGS, Harvard CMT), and the hypo- plane. All of the stations except for occurred on a previously identified center was located at 3.76S and two in Ica are located approximate- seismic gap between the rupture 76.97W, at a depth of 39 km (USGS). ly 00 km to the north in the vicinity areas of the 974 Lima and the Fault rupture propagated south from of Lima. A pattern of higher PGAs 996 Nazca earthquakes (Tavera the hypocenter (Tavera et al., 2007). at soil stations was observed; addi- and Bernal, 2005). The earthquake The finite fault solution of Ji and Zeng tional evidence of site effects is (2007) indicates a seen by the distinctly different spec- rupture plane with tral shapes observed in the four a strike of 324º CISMID stations (Figure 2), which and a dip of 27º, are located in three different soil having approxi- types. Site effects are manifested mate dimensions by significant amplification over of 90 km along period bands that are compatible strike and 95 km with the general site description along dip. The (i.e., shallow, stiff soil deposits at La locations of after- Molina, and soft soils at Callao). shock hypocen- Figure 3 shows the ground motion ters match this record from La Molina. It shows two fault plane (Tav- phases of strong ground motion, era et al., 2007). which correspond to slip along two The shallow dip asperities in the finite fault solution and large width of of Ji and Zeng. The overall shape of the fault plane the acceleration time history is simi- implies that the lar for other ground motion stations. cities most affect- Figure 4. Approximate area of seaward lateral displace- ed by the earth- All the strong motion records had ment of a marine terrace in Canchamana (background quake (Pisco and long durations of strong shaking. image from Google Earth). Ica) lie within the For example, for the La Molina rec- 2 EERI Special Earthquake Report — October 2007 Figure 5. Approximately 0.9 m of liquefaction-induced settlement at a one-story residence in Tambo de Mora. Figure 6. Maximum vertical offset of approximately 3.0 m along the interface between the marine terrace deposit ord, the 5-95% significant duration and the Cañete formation in the Canchamana lateral slide. (Trifunac and Brady, 975) is 0.3 seconds and the bracketed dura- embankments damaged by lateral not firmly established, but appeared tion (duration of ground motion spreading, toppling of power poles to be influenced by the presence of higher than 0.05g) is 98.6 seconds. founded in liquefied soil, rupture of human-made works at a bend in the A duration of approximately 00 water and sewer lines, and disruption Pan American highway. The west- seconds is significantly longer than to port facilities. The liquefaction at ward slope of the marine terrace the duration expected for earth- each of these sites was confirmed by surface was approximately .6 to quakes of similar magnitude from either the presence of sand boils at 2. %. A clear vertical offset (scarp) shallow crustal events (the attenu- the ground surface or wet sand ejecta of variable magnitude was observed ation relationships of Abrahamson in open cracks. The spatial distribu- along much of the geological inter- and Silva [996], developed using tion of observed and reported lique- face between the marine terrace data from shallow crustal events, faction features along the Peru cen- and the Cañete formation (Figure 6). predicts a median duration of 48 tral coast ranged from Villa, just south In addition to the main scarp at the seconds for a Mw 8.0 earthquake). of Lima and approximately 90 km interface, numerous extensional north of the rupture plane, to Paracas ground cracks developed across Geotechnical Aspects in the south (the southern limit of our the marine terrace parallel to the The Pisco earthquake caused a reconnaissance), approximately 24 coastline. In general, the cracks significant amount of soil liquefac- km from the rupture plane, and Ica in were largest (both in terms of hori- tion in the mesoseismal zone which the east, about 40 km from the fault zontal and vertical displacement) resulted in considerable damage to plane. Within this region, liquefaction near the scarp and became smaller urban areas and to the transporta- was widespread wherever the ground towards the coastline. Some crack tion infrastructure. In addition to liq- water table was shallow. The north- widths were as large as m and uefaction, there were a significant ernmost liquefaction site, in the Villa sand ejecta was found inside many number of landslides in road cuts neighborhood of Lima, occurred in a of them. and natural terrain. Landslides were swampy area. responsible for the three-day clos- The massive liquefaction-induced Tsunami ing of the east-west Highway 24A. seaward displacement of a marine The earthquake was centered 35 km The earthquake spawned a wide terrace in Canchamaná, 2.5 km north offshore from Chincha Alta on Peru’s variety of liquefaction failures.