EERI Special Earthquake Report — March 2003 Learning from Earthquakes Preliminary Observations on the Tecomán, Colima, Mexico, Earthquake of January 21, 2003 This report is based on data collect- provided by the National Science ernment. The teams visited the ed after the earthquake by a num- Foundation under Grant 0321781. municipalities of Colima, Manzanillo, ber of teams and individuals. Four Financial support for the EERI team Tecomán, Comala, Coquimatlán, separate reconnaissance groups and for the publication and distribu- Villa de Álvarez, Ixtlahuacan and collaborated in this effort, under the tion of this report was provided by the Armería (shown in Figure 1). recently signed cooperative agree- National Science Foundation grant ment between EERI and the Socie- #CMS-0131895 to EERI’s Learning As of February 20, the effects of the dad Mexicana de Ingenieria Sίsmica from Earthquakes Program. earthquake are as follows: 21 con- (SMIS). (See Acknowledgments for firmed dead; 500+ injured (this is a complete listing of team mem- Introduction an uncertain figure since there has bers.) The Earthquake Engineering not been a systematic confirmation On Tuesday January 21, at 8:06 p.m. Research Institute (EERI) team was of the injured); 13,493 residential local time, a strong earthquake shook headed by Richard E. Klingner of structures reported damaged (many the coastal region of the state of Co- the University of Texas at Austin. of these reports from rapid visual in- lima, Mexico. The earthquake was spections by public teams). Of the strongly felt in the states of Colima, The joint National Center for Disas- 13,493 structures, 11,009 had been Jalisco and Michoacán. The effects ter Prevention (CENAPRED)/Mexi- inspected with the following official of the earthquake were also felt in can Society for Earthquake Engi- results: 2,728 total damage; 4,150 Mexico City. The reported magnitude neering (SMIS) team was headed partial damage; 4,131 safe for occu- varies from M 7.4 (Harvard CMT) to by Sergio Alcocer of CENAPRED. w pancy. Six hundred structures hous- M 7.6 (USGS). The reconnaissance The joint Inter-University Seismic w ing medium and small businesses teams carried out a basic evaluation Research Group (GISS)/SMIS team also suffered some damage. The of the effects of the earthquake, con- was headed by Hugón Juárez Gar- military had established 56 disaster centrating on the response of struc- cía of Universidad Autónoma Metro- assistance centers to provide food, tures and soils, and also on the func- politana – Azcapotzalco. shelter, medical assistance, and tioning of response organizations in public information. different levels of the Mexican gov- The National Science Foundation (NSF)-sponsored geotechnical re- connaissance team was headed by Joseph Wartman of Drexel Univer- sity, Philadelphia, PA, and Adrian Rodriguez-Marek of Washington State University, Pullman, WA. The EERI team arrived in Manzan- illo on January 23 and collaborated closely with the CENAPRED/SMIS team, which initiated reconnais- sance activities on January 22. The GIIS/SMIS team arrived in Colima on January 23 and visited damaged sites in the state of Colima as well as in the neighboring states of Jal- isco and Michoacán. The NSF team arrived on January 25 and coordi- nated with the EERI team already on the ground. Figure 1 - Epicentral locations of main shock and aftershocks as Financial support for the NSF geo- reported by the USGS and SSN. Included also is the epicentral technical reconnaissance team was location of the Mw 8.0 1995 Manzanillo earthquake. 1 EERI Special Earthquake Report — March 2003 EERI Special Earthquake Report — March 2003 Seismicity can Plate, and the faster Cocos Ground Motions plate is moving in a similar direction Just as the initial reports on the at a rate of about 45 mm per year The Manzanillo Power plant record magnitude of the earthquake vary, (USGS http://neic.usgs.gov/neis/ is the only strong-motion record of so does the reported location of the bulletin/neic_phac.html). The earth- the earthquake obtained within 100 hypocenter. Table 1 lists the source quake was an interplate subduction km of the rupture plane. Various parameters of the event as reported event at the contact between the records at distances greater than by various agencies. Figure 1 plots North American plate with either the 120 km were obtained from strong the location of the epicenters as re- subducting Cocos or Rivera plates. motion arrays in Guadalajara and ported by various agencies, along Mexico City. The Manzanillo Power with the locations of aftershock epi- The event fi lled a seismic gap located Plant record registered maximum centers reported by the Servicio accelerations of 0.263g in the EW between the rupture zones of the Mw Sismológico Nacional de México 8.0 1995 Manzanillo earthquake and direction, 0.329g in the NS direction, (SSN). and 0.191g in the vertical direction. a Mw 7.6 earthquake in 1973 (Figure 2). A fault plane solution by Yagi Strong shaking lasted approximately The signifi cant discrepancies in (http://www.iisee.kenken.go.jp) 30 seconds. It was reported that moment magnitude and epicenter from the International Institute of earthquake movement ruptured the location obscure any preliminary Seismology and Earthquake Engi- power plant’s main 2.4 m diameter conclusions about the unusual dam- neering (IISEE), Tokyo, is shown in cooling water intake pipe, which age distribution. There was much Figure 3. The dimensions of the rup- caused the plant to operate at a re- greater damage to the inland city of ture plane are approximately 80 km x duced capacity in the days after the Colima than the coastal city of Man- 50 km. main event. zanillo (which is closer to the rup- ture zone as defi ned by aftershock hypocenters) while, in contrast, damage from the 1995 Mw 8.0 Manzanillo earthquake was largely focused near the epicentral region. The earthquake occurred near the juncture of three tectonic plates: the North American Plate to the north- east, the Rivera Plate to the north- west, and the Cocos Plate to the south. Both the Rivera Plate and the Cocos Plate are being subducted beneath the North American Plate. Figure 2 - Approximate location of rupture planes The slower-subducting Rivera Plate of subduction zone events since 1973 (http:// is moving northwest at about 20 mm www.ssn.unam.mx/Colima030121/index.html). per year relative to the North Ameri- 2 3 EERI Special Earthquake Report — March 2003 EERI Special Earthquake Report — March 2003 Site Effects Damage surveys in the conjoined cities of Colima and Villa de Álvar- ez indicated locations of damage concentration around the neighbor- hoods of San Isidro (Villa de Álvar- ez) and Lomas de Circunvalación (Colima) (see Figure 4). In addition, damage to adobe housing in down- town Colima was extensive. Dam- age surveys were carried out using PQuake software (Georgia Institute of Technology), which directly inte- grates digital photography and handheld GPS technology to facili- tate documenting, mapping, analyz- ing, and visualizing damage data. The use of PQuake permitted a digital data set of the earthquake Figure 3 - Fault plane solution by Dr. Y. Yagi (http:// effects to be created in a timely iisee.kenken.go.jp/staff/yagi/eq/colima/colima.html). manner. Damage surveys were per- formed either by assigning an aver- foundation material. Intense damage the coastal city of Manzanillo and in age damage index (D0 = no dam- in the Lomas de Circunvalación the neighboring cities of Villa de Ál- age, D5 = collapse) to a whole block neighborhood is limited to a few city varez and Colima, located approxi- (Block Survey), or by assigning blocks. Construction patterns do not mately 80 km inland. damage indices to individual build- vary in this neighborhood, suggesting ings. that damage is due to localized Liquefaction may have also oc- ground-motion amplification, suspect- curred in the sparsely inhabited re- The San Isidro neighborhood is lo- ed to be associated with fills. gion between these two urban cen- cated near the Arroyo de Pereira, a ters, though this was not confirmed small creek running north to south Soil Liquefaction during the reconnaissance. In Man- across Colima/Villa de Álvarez. zanillo, home to one of the largest Soil liquefaction caused damage in Most of the damaged area overlies highly heterogeneous fill. Evidences of liquefaction were found in areas of high damage concentration. Sig- nificant ground settlement was ob- served at some locations, possibly due to collapse of poorly compacted fills (Figure 5). There were numer- ous reports of open-pit sand mining earlier in the 1900s at this location. Poor filling of these pits could ex- plain localized zones of large sur- face settlement. Although construc- tion quality in the San Isidro neigh- borhood is poor, other neighbor- hoods with similar construction did not suffer as much damage. The Lomas de Circunvalación neighborhood is underlain by vol- canic debris avalanche deposits that also underlie most of the north- central section of Colima. While this unit is highly heterogeneous, it is re- Figure 4 - Damage survey map of the city of Colima indicating areas portedly stiff and performs well as a of high damage concentration. 2 3 EERI Special Earthquake Report — March 2003 EERI Special Earthquake Report — March 2003 Figure 5 - Large settlements in a house in the San Isidro neighborhood, possibly due to collapse of poorly consolidated fills. ports in Mexico, liquefaction was A majority of the waterfront liquefac- settlement, and lateral spreading, largely confined to waterfront sites, tion sites in Manzanillo were marked alone or in combination, are sus- including multiple locations at the by lateral spreading of the ground pected causes of other damage to commercial shipping port, a public toward the free face.