Baja California) Earthquake of April 4, 2010

EERI Special Earthquake Report — July 2010

The Mw 7.2 El Mayor Cucapah (Baja California) Earthquake of April 4, 2010

The Earthquake Engineering Re- throughout Baja California, Southern The northern half of the rupture search Institute (EERI) coordinated California, Arizona, and Nevada. The propagated 55 km through an imbri- reconnaissance teams in the dam- epicenter was approximately 47 km cate stack of east-dipping faults in aged areas. The California Seismic SSE of Mexicali, BC, 51 km SSE of the Sierra Cucapah. In the southern Safety Commission, Degenkolb, Calexico, California, and 180 km E of part, the rupture extends 20 km Exponent Failure, GeoHazards Inter- San Diego (see Figure 1). This is the along the Laguna Salada and Pes- national, Hilti North America, JP Singh largest earthquake in the area since cadores faults, where it reached a and Associates, Kleinfelder, Parsons, the Laguna Salada quake in 1892. maximum displacement of approxi- PSOMAS, Simon Wong Engineers, mately 250 cm of right-lateral strike Tobolski/Watkins, and the University This brief report describes fault rup- slip. The amount of dip slip is vari- of California San Diego participated ture, liquefaction and lateral spread, able and changes polarity along the in these efforts. The EERI teams and the effects of the earthquake on Laguna Salada fault before becom- worked closely with GEER (Geo- buildings, bridges, water and waste- ing predominantly east-side-down, Engineering Extreme Events Recon- water systems, nonstructural compo- with maximum offsets of 150 cm naissance). The surface faulting nents, agriculture and the economy. along the Pescadores fault. This mapping was led by researchers at Comprehensive reports on the earth- rupture terminates in the high ele- Centro de Investigación Científica y quake by EERI and GEER can be vations of the sierra and jumps de Educación Superior de Ensenada found at http://www.eqclearinghouse. (CICESE) in México and at San Diego nearly 10 km north in a left step- org/20100404-baja/ and http://www. State University. Geotechnical recon- over to the Borrego fault. Addition- geerassociation.org/Post_EQ_ naissance and mapping was led by ally, the 1892 segment of the north- Reports.html, respectively. researchers at UCLA, the U.S. Geo- ern Laguna Salada fault re-broke logical Survey, and the California with minor (10-30 cm) dip slip along Geological Survey. Surface Faulting a segment that is adjacent to the Support for the reconnaissance was Surface rupture extends about 100 primary Borrego rupture. provided by local authorities in Mexi- km from the northern tip of the Gulf of cali, including the Department of Civil California to the international border Figure 3 shows the maximum mea- Protection; State Center of Control, and comprises two distinct geomor- sured displacement along the Bor- Command, Communication, and phologic and structural domains. As rego fault in Borrego Valley, which Computing; Baja California State shown in Figure 2, the rupture is Police; SIDUE (Secretary of Infra- complex, with breaks along CISN ShakeMap for Sierra El Mayor Earthquake structure and Urban Development multiple fault strands, including Sun Apr 4, 2010 03:40:42 PM PDT M 7.2 N32.26 W115.29 Depth: 10.0km ID:14607652 of Baja California); and CICESE. A minor re-rupture of the scarps 33.5û complete list of team members is associated with the 1892 Salton City provided at the end of this report. Laguna Salada earthquake Ocotillo Wells 33û Brawley The research, publication and distri- and several other older events. The southern part of the rup- El Centro bution of this report were funded by Yuma Mexicali the EERI Learning from Earthquakes ture consists of a zone of Tecate 32.5û project, under grant #CMMI-0758529 distributed fracturing and lique- San Luis R o Colorado from the National Science Foundation. faction that cuts across the Guadalupe Victoria Fault rupture and geotechnical engi- Colorado River delta. Indi- 32û neering aspects reported here are vidual fractures vary widely in kmEnsenada based on GEER studies supported by orientation and have relatively 0 50

NSF under Grant #CMMI-1034831. short strike lengths of as small 31.5û -117û -116û -115û as hundredths of meters. The Map Version 12 Processed Tue May 18, 2010 03:14:18 PM PDT, -- NOT REVIEWED BY HUMAN

PERCEIVED Introduction zone itself may be related to SHAKING Not felt Weak Light Moderate Strong Very strong Severe Violent Extreme POTENTIAL DAMAGE none none none Very light Light Moderate Moderate/Heavy Heavy Very Heavy faults that bound the eastern PEAK ACC.(%g) On Sunday, April 4, 2010, at 3:40 <.17 .17-1.4 1.4-3.9 3.9-9.2 9.2-18 18-34 34-65 65-124 >124 PEAK VEL.(cm/s) <0.1 0.1-1.1 1.1-3.4 3.4-8.1 8.1-16 16-31 31-60 60-116 >116 margin of the Sierra El Mayor, INSTRUMENTAL p.m. local time (22:40:42 UTC), an INTENSITY I II-III IV V VI VII VIII IX X+ but field relationships are un- Mw 7.2 earthquake struck northern clear, and the zone of more in- Figure 1. Distribution of intensities. Star Baja California (BC), México, locat- tense fracturing diverges signifi- shows location of epicenter (http:// ed at 32.259ºN, 115.287ºW at a cantly from the mountain front earthquake.usgs.gov/earthquakes/ depth of about 10 km. It was felt toward the south. eqinthenews/ 2010/ ci14607652/#maps).

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ture to expand in the near surface. This rupture illustrates the complexity that can develop when a rupture propagates through a network of high- and low-angle faults that accommodate the three-dimensional strain of transtensional plate margin shearing.

Ground Motions The main event on April 4, 2010, was recorded by 497 strong motion instruments in California (USA) and Baja California (México). The California strong motion instruments are owned and maintained by California Strong Motion Instru- mentation Program (CSMIP) and the US Geological Survey, although several smaller networks also oper- ate in the region. The Baja Califor- Figure 2. View of earthquake region showing location of mainshock hypo- nia strong motion instruments, the center, aftershocks in first 48 hours, and mapped locations of surface rupture Red de Acelerografos del Noroeste (moment tensor and aftershock locations from SCSN web site: http://www. de México (RANM), are owned and scsn.org/2010sierraelmayor.html). maintained by CICESE. Strong motion records obtained in was about 3.1 m of strike slip and the Paso Superior and extending an California are available at http:// another 2 m of down-to-the-east additional 10 km farther north. The www.strongmotioncenter.org and dip slip on a nearly vertical fault, Paso Superior fault is well exposed at http://gees.usc.edu/ROSRINE/, yielding oblique slip of nearly 4 m. Highway 2, where it clearly involves while records obtained in Baja Cali- A low-angle detachment intersects a low-angle detachment. Scarps near fornia are available at http://resnom. the footwall of the central portion the fault trace accommodate dip slip, cicese.mx/reportes/preliminar/. of the Borrego fault at a segment and nearly twice as much strike-slip The largest peak ground accelera- boundary, and rupture bifurcates is spread across a 100-150 m wide tion (PGA) of about 59% g was re- with a splay that follows the trace of zone of cracking and secondary fault- corded in El Centro-Array 11, Cali- the detachment in a more westerly ing to the east. fornia (RRUP = 21.2 km), and the direction. Over the next 6 km to Part of the complexity of the rupture second largest PGA of about 54% the north, rupture steps left across can be attributed to interaction with g was recorded in Michoacan de a 2-km-wide zone, before finally detachment faults that allow the rup- Ocampo MDO station, Baja Califor- consolidating on a fault named

Figure 3. Panoramic mosaic of the El Mayor-Cucapah earthquake rupture along the Borrego fault in Borrego Valley, Sierra Cucapah, Baja California, México. (photo: Tom Rockwell, photo-stitched by Karl Mueller)

2 EERI Special Earthquake Report — July 2010 nia (RRUP = 17.5 km). The ground 32.7 cm and 61.0 cm/sec respectively from surface waves generated motion was approximately 2-5% g (Munguia et. al. 2010). within the basin (GEER 2010). in the San Diego area and approxi- The ground motions recorded at MDO The Imperial and Mexicali valleys mately 1% g in the Los Angeles and El Centro 11 stations bear many are soft sediments characterized area. similarities to recordings from two sta- by values of VS30 of less than 250 Figure 4a presents the acceleration, tions located at almost identical loca- m/sec. Displacement and velocity velocity, and displacement time his- tions on the Imperial Fault during the waveforms are rich in long-period tories of the main event recorded 1979 Imperial Valley earthquake — motions that are consistent with soft at El Centro — Array 11, McCabe the Holtville Post Office (Figure 4c) soil deposits and/or basin effects. School. The PGD and PGV were and El Centro Array 3 (Figure 4d) The seiche effects observed in Fig 53.1 cm and 62.9 cm/sec respec- (Singh 1985). Lagoon as well as the sloshing of tively. Figure 4b presents the accel- water and sewer tanks and clari- The main difference is longer dura- eration, velocity, and displacement fiers in some locations in Imperial tions with long surface wave tails that time histories of the main event re- Valley were likely amplified by this are a result of a larger magnitude corded at MDO station, Baja Cali- long-period motion, particularly earthquake. Significant long period fornia. The peak displacement where sloshing periods coincided energy content at an apparent period (PGD) and velocity (PGV) for the with the period of the ground mo- of 6 to 7 seconds in the Imperial Val- E-W component were calculated at tion. However, due to the lack of ley basin is thought to result in part

(a) (c)

(b) (d)

Figure 4. Ground motions recorded during the 2010 and 1979 earthquakes (a) El Centro Array 11, McCabe School, 2010, California; (b) MDO Station, 2010, Baja California, México; (c) Holtville Post Office, 1979, California; and (d) El Centro Array Station 3, 1979, California.

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Figure 5. ▲ Damage to irrigation canal in Mexicali Valley.

Figure 6. Unseated span of railway bridge near Guadalupe Victoria.►

instrumentation throughout the basin, the extent of and variation of this long period response in differ- fault rupture), and Imperial Valley At parallel bridges that cross the ent locations throughout the valley (northeast of faulting). South of the Colorado River approximately 6 km is not clear. border, liquefaction was widespread, southeast of Guadalupe Victoria, Perhaps future three dimensional particularly in the largely agricultural BC, the railway bridge collapsed modeling of basin effects as well as Mexicali Valley near the epicenter, when a simply supported span was the study of the response of long where sand boils, lateral spreading, unseated by liquefaction and lateral period systems in this earthquake settlement, ground fissures, and spreading of surrounding soil (Fig- and others could help improve the flooding were observed. Loose satu- ure 6); the immediately adjacent characterization of these phenom- rated fine sand and non-plastic silts and parallel highway bridge did not ena. and shallow groundwater contributed collapse, but suffered damage due to liquefaction. Impacts from liquefac- to foundation settlement and strong The main event was also recorded tion included topographic warping of ground shaking. Ground crack at instrumented buildings and the previously flat farmland, and dam- widths were measured along the bridges in El Centro and San Diego age to irrigation canals due to settle- eastern margin of the flood plain, as well as the Los Angeles area. In ment, lateral spreading, and ejected and the sum of the crack widths El Centro, a peak acceleration of sand filling the canals (Figure 5). was nearly 5 m, indicating signifi- about 93% g and a peak displace- cant lateral spreading displace- Many fields of wheat and hay became ment of 34 cm were recorded at ments affecting the bridges. the roof of the El Centro one-story submerged due to subsidence and hospital. the high ground water table through- At a group of buildings and a ped- out the region. Liquefaction was so estrian bridge at the Universidad Liquefaction widespread throughout the valley that Autónoma de Baja California cam- the reconnaissance team could not pus, constructed in the New River The geology of the region consists adequately quantify its extent during flood plain, the buildings and bridge of soft lacustrine and alluvial mate- the short time it was present. Hence, were damaged by liquefaction- rials with shallow groundwater in our observations focused on record- induced settlement and some small the Mexicali Valley (east of fault ing detailed perishable data at a small lateral deformations. The buildings rupture), Laguna Salada (west of number of sites of engineering interest. were founded on pile foundations

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its diversion from the All American Canal northeast to Fites Road, approximately 6 km southwest of Brawley. Liquefaction of relatively fine-grained soils was observed at the foundation of the All Ameri- can Canal aqueduct over the New River. Liquefaction accompanied by lateral spreading on both sides of the Rosita Canal northwest of Holtville disrupted the canal and allowed seepage onto adjacent agricultural fields.

Other notable damage included liquefaction and lateral displacement of the dam embankment and adjoining Drew Road at the west-

Figure 7. Settlement of base slab beneath four-story steel braced frame structure at Universidad Autónoma de Baja California, Facultad de Ciencias Administrativas site. that showed no signs of liquefac- Alamo rivers. Liquefaction was most tion-induced settlement, but the common in the southwest portion of floor slab separated from the walls Imperial Valley, though a significant of the building (Figure 7). Liquefac- exception was observed northwest tion and lateral spreading also dam- of Holtville. Most road closures were aged many homes along the Rio associated with crossings of the New Hardy River in the Mexicali Valley to River or its tributaries, and were pre- the south of the epicenter. dominantly caused by liquefaction of bridge approach fills and/or the In the Laguna Salada, a sub-sea- soils underlying the fills. This was the level basin west of Mexicali, the case at Worthington, Drew, and rupture features from the 1892 Mw Brockman roads where they cross the 7.1 earthquake have been mapped New River, and at Brockman Road along the eastern side. Earthquake- where it crosses induced liquefaction from the 2010 Figure 8. (a)  Liquefaction-related lateral spread of the Greeson Drain. quake created sand boils and fis- the crest of the Sunbeam Lake Dam (photo: Cindy Prid- Where Lyons sures, bringing water to the surface more on 4/8/10). (b) ▼ Sinkhole forming on the Sun- Road crosses the along the eastern side of the Lagu- beam Lake Dam adjacent to the outlet weir. New River, there na Salada basin adjacent to the was liquefaction- Sierra Cucapah mountain range. induced lateral Reports from subsequent after- spreading in nat- shocks confirmed that additional ural soils and road saline groundwater was brought fill 100 m east and to the surface, flooding dirt roads 200 m west of the along the eastern dry lake basin. bridge, but the The ponding groundwater quickly bridge structure evaporated and created salt flats. and approach fills GEER conducted reconnaissance were undamaged. in the Imperial Valley within one Most damage to week of the mainshock, concentrat- irrigation canals ing on easily accessed locations was concentrated along major and minor roads, can- on the Westside als and drains, and the New and Main Canal, from

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tal shaking intensity north of the border. Of the approximately 31,000 buildings in the region, 63 were red tagged (0.2%) out of 431 total buildings that received safety assess- ments (1.4%). Damage was concentrated in known vulnerable building types such as mobile homes and wood frame dwellings on crip- ple walls, unreinforced masonry buildings, and multi-unit residential buildings that rely on plaster finishes for earthquake resistance. Several rare older homes constructed with adobe were also moderately damaged. South of the border: In Mexicali, a five-story concrete shear wall park- ing structure under construction at Figure 9. Breach in Fig Lake levee created by liquefaction-related lateral the time had floors collapse. It con- spread ground failure and settlement. sisted of precast concrete double- tees, spandrels, and columns. A ern end of Sunbeam Lake south of of Mexicali and in older commercial topping slab with dowels was ex- Seeley (Figure 8), and liquefaction- portions of Mexicali. Baja California pected to provide out-of-plane induced slump of a levee that al- State Police reported 4,389 residenc- anchorage for the perimeter span- lowed overtopping of the levee es with major damage (1.3% of the drels. The concrete topping had not likely by seiche waves generated 340,000 buildings) in the Mexicali re- yet been poured at the outer bays in Fig Lagoon (Figure 9). Notable gion, which has a population of over to provide connectivity to the shear sites that liquefied during the 1979 1 million residents. Most modern walls, and the precast spandrels Imperial Valley earthquake did not homes are concrete frames with clay and columns displaced excessively show evidence of ground failure brick or concrete masonry infill walls; in the north-south direction; this un- in this event, including the Wildlife many older homes are built with seated the double tees from their liquefaction array and the Heber adobe. bearing pads and resulted in col- Road site. lapse of the floors. Damage to buildings north of the border was scattered. A population of At a two-story concrete frame high Structures approximately 90,000 lives in the school in Mexicali, built in 1958, Damage to buildings south of the region of MMI VII-VIII instrumen- shear cracks developed in the col- border was concentrated in the agricultural communities to the south

Figure 10. Short, nonductile concrete column severely damaged in high school building. Figure 11. Soft story apartment with plaster walls in El Centro.

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wood frame walls with plaster finishes to resist earthquake and wind forces (Figure 11). Longitudinal plaster walls on the east side at the north end of the building experienced a residual drift between 1 to 2 inches. The building was reported by neigh- bors as deteriorating with significant aftershocks, and government officials barricaded it to discourage access to the building’s perimeter. A two-story nonductile concrete frame building in El Centro with unreinforced brick masonry infill walls was severely damaged (Figure 12). Its brick mortar joints had been repaired and one window opening was infilled with concrete masonry units Figure 12. Concrete infill with a partial loss of infill brick walls. after significant damage in the 1987 umns and infill walls. The shear fail- climate was too hot for education in Superstition Hills earthquakes (EQE, ure of the exterior columns can be tents or mobile classrooms without 1988). The building was also dam- attributed to the short-column effect air conditioning. Officials anticipated aged and repaired after the 1940 introduced by the partial-height infill reopening schools by the end of May. earthquake (Steinbrugge, NISEE, walls. The exposed concrete inside 1940). Cracks in concrete columns At the Universidad Autónoma de Baja some of the damaged columns in- and beam-column joints on three California, a two-story building had dicated poor concrete quality, i.e., elevations of the building depict a cracking of the masonry infill, spalling poor consolidation and smooth variety of responses of individual of the stucco-like exterior coating, aggregates (Figure 10). Retrofitted components. This building is worth and spalling of the tile finish. Much columns performed satisfactorily, further study regarding the efficacy damage to exterior finishes was ob- but in some cases had damage be- of prior repairs, particularly since served in the vicinity of interstory hor- low jacketed portions. The masonry nearby ground motion recordings izontal joints, most likely due to differ- infills were damaged by a combina- are available. ential horizontal movement. tion of severe diagonal cracks and bed-joint sliding. North of the border: The Cottonwood Nonstructural Components Circle apartment building in south El and Systems The state government decided to Centro has an irregular configuration delay the return to school for 13,000 Nonstructural damage was pervasive with a soft and weak story along both students in the 57 schools affected in the interior of buildings, both in axes of the building. It relies on light by the earthquake because the the U.S. (Calexico and El Centro)

Figure 13. Mexicali campus of UABC: (a) extensive ceiling damage at the Electronics and Computer Laboratory building and (b) damaged CMU infill in the new eastern annex to the Engineering Institute buildings.

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Figure 14. Typical interior damage to ceilings at the Medical Plaza building in El Centro. Figure 15. Collapse of exterior soffit at Jefferson Elementary School. and in México (Mexicali); it caused business closures and significant The El Centro Regional Medical Cen- stations are located on the com- disruption as well as financial losses. ter (ECRMC), a community hospital plex, one of which recorded a Commonly observed were damaged owned by the City of El Centro, has PGA of 0.38g and associated glazing, ceilings, partition walls, pip- one- and two-story wings, construct- Sa(T=0.3sec) of 1.4g. Despite ing systems, HVAC ducts, and other ed in 1956 and 2003, respectively. A these rather large accelerations, the building services equipment. In many neighboring Medical Plaza building hospital performed quite well. instances, building operations were and central plant serve the hospital. Most modern buildings in Calexico severely hampered or halted due to Minor nonstructural damage was ob- performed well, but in the historic nonstructural damage alone. One served in the main hospital and to its downtown, five blocks were closed hospital wing in the U.S. and two central plant, while the Medical Plaza following the earthquake due to hospitals in Mexicali were partially building (Figure 14) was red tagged widespread damage to façades, evacuated due to nonstructural largely due to nonstructural damage. windows, parapets, plaster, or damage. Schools were widely affect- Fortunately, no injuries were reported. stucco, and other nonstructural ed, including a number of elementary The ECRMC is an interesting case, as elements. A USGS strong-motion schools in Calexico and a university three strong-motion instrumentation station located at the undamaged campus in Mexicali. The Mexicali campus of the Univer- sidad Autónoma de Baja California (UABC) is located approximately 44 km NE of the epicenter of the quake. The university was established in 1957 and has upwards of 16,000 students. In addition to structural damage, extensive nonstructural damage was observed, primarily in the form of ceiling, partition, and contents damage. All but one of 11 buildings on campus were closed, largely due to nonstructural damage. In the rooms of some buildings, over 80% of the ceiling tiles failed (Figure 13a). The buildings were mostly short (typically 2-3 stories) and constructed of masonry block or concrete frame with block infill. Damage to infill walls was also pervasive on the campus (Figure 13b). Figure 16. Fallen light fixtures and ceiling system components.

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week to make repairs. It is worth noting that the final posi- Some repairs were tion of the piers after the earthquake complicated by con- resulted in large gaps between the cerns over asbestos. inside face and soil on both ends of the bridge. Sidewalks were also Bridges cracked at the piers crossing the centerline of the bridge. Further, The EERI team ob- hanger rods sloping away from the served damage at the mid-span at both ends of the bridge, pedestrian bridge at in both planes of hangers, were UABC, a newly con- buckled. These residual deforma- structed 175-ft. steel tions are clear indications that the arch tied to large diam- bridge has in fact elongated horizon- eter concrete piers. At tally between arch pins. It is also the ends of the super- apparent that failure of the tie did structure deck, trans- not result in collapse, and therefore verse tubular steel redundant load paths were active. struts were designed Figure 17. UABC pedestrian bridge strut-connection to provide longitudinal On Highway 2, about 15 miles west failure resistance to seismic of Mexicali, an overcrossing was forces. The end plate of the struts damaged. The bridge is a 250-ft. Calexico fire station measured a was rigidly connected to the interior long two-span precast, prestressed PGA of 0.27g, with the resulting face of the piers. All welds of the (PC/PS) concrete girder bridge on Sa(T=0.3sec) of 0.74g. Buildings anchor bolts connecting one strut to bent cap and round concrete col- in downtown Calexico are pre- the concrete piers had completely umns supported on drilled shafts. dominantly single-story wood with fractured. Concrete columns sup- The damage observed included veneer, concrete masonry or brick porting the spiral ramp structure shear key cracking extended into construction, all with anticipated and the anchor bolts were cracked. the bent cap, expansion joint dam- periods of less than 0.5 seconds. There was also liquefaction of the age associated with superstructure Jefferson Elementary School in soil surrounding the foundation. translational and rotational move- Calexico, constructed in the 1960s, The fracture may have been caused ments, crushing and settlement had significant nonstructural dam- by excessive longitudinal seismic of the slope paving at abutments, age. Approximately 1200 square forces on the strut connections, spalling and cracking of concrete feet of exterior plaster ceiling soffits combined with rotational demands pedestals for the girder ends at overhanging walkways fell in a pro- as a result of pier movement in liq- abutments, and permanent distor- gressive fashion (Figure 15). Fortu- uefied soil (Figure 17). tion of bearings pads. nately, schools were not occupied at the time of the earthquake and no one was injured. Other buildings showed signs of plaster soffit distress, and while the soffits did not collapse, they will likely have to be retrofitted before reopening the school. The soffit collapses in some cases blocked classroom doors from opening and in three locations sheared off door knobs and a hose bib. In some of the classrooms and a multi-purpose room, light fixtures and parts of ceiling systems fell onto desktops and floors (Figure 16). Of the 82 public schools in Imperial County, California, many reported minor damage to building contents and nonstructural systems, and Figure 18. Fissure and sand boils in alfalfa field southeast of Cucapah, Baja took advantage of spring break California, México.

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lack of irrigation and are likely to be lost for this season. In addition, mas- sive sand boils and sand sheets blanketed portions of fields, and large-scale lateral spreading created scarps and fissures that crossed fields (Figure 18). The Baja Califor- nia government reported that the earthquake also caused permanent regional ground tilting, which will disrupt gravity-controlled irrigation. The extensive damage in the agricultural portion of the Mexicali Val- ley may be an indicator of future Figure 19. El Centro damaged secondary clarifier and well assembly (photo: earthquake impacts in some agri- Jose Angel). cultural and levee-protected areas in seismically active areas of the On Highway 5, many two-span over- Water and Wastewater U.S. crossings had significant approach Systems Damage to water systems in Mexi- roadway settlements and partial fail- cali may have contributed to the ures of reinforced embankment soils. The quake damaged water and waste- increase in flow of the New River These bridges were also recently water treatment plants, irrigation can- where it crosses into California, but constructed and have slope paving als, and the encasement of the New as of May 12, 2010, the extent of on the west side, with highly rein- River. In the Imperial Valley, damage direct and indirect damage to farm- forced soils in the east abutment. to earthen canals, apparently related lands in the Imperial Valley had not Most are oriented in the east-west to lateral spreading and liquefaction, been consolidated. On April 14, direction. No shear key failures was widespread but not severe, with representatives from the Imperial were found, but significant bridge the exception of the All American Irrigation District (IID) discovered movement and approach settlement Canal crossing of the New River. No that there was leakage between the were observed in the longitudinal significant damage to drainage sys- northern headworks and the spill- direction due to liquefaction and tems for farms has been reported. In way adjacent to the All American lateral spread. the Mexicali Valley, there was wide- Canal siphons crossing the New spread damage to irrigation canals, The earthquake caused collapse of River, downstream from the Calex- fields, and towns due to ground fail- ico wastewater treatment plant. one span of Puente San Felipito, a ures and earthquake-related flooding. railroad bridge over the Colorado Portions of the area were inundated The siphons are a critical compo- River constructed in 1962. It is lo- with water from liquefaction-induced nent of the canal, since they allow cated approximately 5 miles south- sand boils, some of it reportedly sa- water to cross the New River to east of Guadalupe Victoria, near the line, sulfurous, or otherwise contami- supply the IID with water for the Baja California and Sonora border. nated. Localized sections of roads, western one-third of its coverage The bridge is approximately 650 fields, and towns were also inundated area. The siphons were in opera- feet long, spanning the river with with water from overflowing canals. tion during the 1979 Imperial Valley multiple spans, including a PC/PS earthquake, but were not reported concrete girder supported on con- Liquefaction and lateral spreading to have been damaged. There crete piers, with oblong sections caused cracking, settlement, and was significant damage to earthen supported on piles. Complete un- slumping of unreinforced concrete- canals in the 1979 quake, where seating of the girders due to both lined irrigation canals (refer back to the Imperial fault crossed the canal. transverse movement of the super- Figure 5). The Baja California govern- structure and longitudinal pier ment initially estimated that 57 km of Due to the potential loss of water for movement was evident. The super- major canals, 350 km of minor can- the communities of Westmoreland, structure did not have any shear als, and 380 km of drainage channels Brawley, and Seeley and farmlands keys or any sizable anchorage to were damaged. west of the siphons, as well as the potential for flooding properties near restrain lateral or longitudinal move- Many crops in the fields at the time of ments relative to the piers. the siphons, the IID had representa- the earthquake, predominantly wheat tives from the Los Angeles Office and alfalfa but also cabbage and new- of the United States Army Corps of ly planted cotton, were wilting due to Engineers (USACOE) inspect the

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Figure 20. Ground shaking intensity maps from three significant earthquakes in the region: above left 2010; above right 1979; bottom left 1940.

4 million gallons. Economic Losses The plant produc- tion capacity was As of May 8, 2010, the Baja Califor- down 50% after nia State Police estimated US$425 the earthquake. million in direct losses south of the The lack of water border. As of April 21, CalEMA es- treatment capacity timated $91 million north of the for the upcoming border. However, the extent of dam- summer months is age to the water systems, the ensu- a concern, since ing floods in Baja California, and the water usage is sig- impacts on agricultural irrigation, nificantly increased particularly in Baja California, are beyond spring not fully estimated at this time. The headworks and spillway area on water usage. loss of farming capacity south of April 14. At the time of this writing, the border could cause long-term the extent of the damage as well as At the El Centro wastewater treat- economic disruption to the region, the scope of the repairs, their cost, ment plant, there was structural dam- both north and south of the border. and time required to make repairs age to one primary clarifier and to two The unemployment rate in Imperial on the canals are not known. secondary clarifiers. The baffles of County, California, before the earth- the primary clarifier were sheared off quake was 27%, and an additional In Calexico, the wastewater treat- of the clarifier and broke. The clarifier 250 claims for unemployment due ment plant had damage to a 36-inch also had some relatively superficial to earthquake damage had been diameter inlet feeder line that small cracks. The center well of the received by April 21, 2010. crossed the New River to the plant. secondary clarifier No. 2 was twisted The pipe was discharging between (Figure 19). The center column of the Preliminary Conclusions 200,000 to 300,000 gallons per day secondary clarifier No. 3 dropped of wastewater into the New River about 5 inches. There is structural The border region’s five most recent before being bypassed on April 9. damage to the concrete walkways significant earthquakes have many There was also damage to primary and inspection bridges of the aeration similarities. Both the M6.9 1940 and secondary clarifiers, lagoons, tanks. Interestingly, the damage to and M6.5 1979 earthquakes struck and berms (lateral spreading), and one of the clarifiers was similar to that on the Imperial fault, northeast of sludge beds. Three water storage reported in the 1979 Imperial County Mexicali. Two strong earthquakes (M6.2 and 6.6) struck in 1987 to tanks were also damaged; they Mw 6.5 earthquake. varied in age from 60 to five years the northwest in the Superstition old, and in capacity from 1 million to Hills. The 2010 earthquake crossed

11 EERI Special Earthquake Report — July 2010

over a series of faults southwest Team Members risky in terms of access and guidance of Mexicali, with a strike similar in to sites of interest in unknown terri- orientation to the Imperial fault. The EERI team: Jorge Meneses, team tory. Without local support from indi- leader, Kleinfelder; Robert Anderson, ShakeMaps from the 2010 and viduals and organizations in México, California Seismic Safety Commission; 1979 earthquakes and an isoseis- our reconnaissance efforts would not José Angel, California Regional Water mal map for the 1940 earthquake have been possible. The list of those Quality Control Board, Palm Desert; who assisted us is too long to include (north of the border) are provided in Jeremy Callister, Degenkolb Engineers; Figure 20. in this brief report, but can be found Mark Creveling, Simon Wong Engineer- on the following web pages: http:// The 1940 earthquake was believed ing; Curt Edwards, PSOMAS; Lisa Ever- www.eqclearinghouse.org/20100404- to have caused $5 to 6 million in ingham, Degenkolb Engineers; Víctor baja/ and http://www.geerassociation. damage (Ulrich 1940) — $77-$92 Garcia-Delgado, DSA; Arnold Gastelum; org/Post_EQ_Reports.html. million in today’s dollars. The 1979 University of California, San Diego (UCSD); Gabriele Guerrini, UCSD; The EERI Reconnaissance Report earthquake caused an estimated Ricardo Hernandez, Degenkolb Engi- on the 1979 Imperial Valley quake $30 million (EERI 1980) — $89 neers; Matthew Hoehler, Hilti North is an excellent source of information million in today’s dollars (CPIIndex America; Tara Hutchinson, UCSD; and was very instructive for the 2010 Measuringworth.com). Nine were David King, California Seismic Safety reconnaissance team. “The Impe- killed and 20 seriously injured in Commission; Ioannis Koutromanos, rial Valley Earthquakes of 1940,” by 1940 (Ulrich 1940). No deaths and UCSD; Betsy Mathieson, Exponent Franklin Ulrich, was also helpful and nine serious injuries were reported Failure Analysis Associates; Silvia provides an interesting glimpse of in 1979 (EERI 1980). In 2010, two Mazzoni, Degenkolb Engineers; Gary earthquake reconnaissance docu- deaths and approximately 100 injur- McGavin, California Seismic Safety mentation prior to EERI’s studies. ies were reported south of the bor- Commission; Flavio Mosele, UCSD; All photos by team members unless der, and there were 45 injuries re- Juan Murcia, UCSD; Hussein Okail, otherwise noted. quiring hospital visits north of the UCSD; Steven Okubo, Exponent Fail- border. ure Analysis Associates; Chris Poland, Degenkolb Engineers; Janise Rodgers, References However, while there are similarities, GeoHazards International; Travis Sand- Earthquake Engineering Research there is plenty of evidence that fu- ers, Degenkolb Engineers; JP Singh, Institute (1980), Imperial County, ture earthquakes may differ in their JP Singh & Associates; Heidi Stenner, California, Earthquake, October 15, effects. In 2010, the most severe Exponent Failure Analysis Associates; 1979. EERI, February 1980. shaking was focused on lightly pop- Majid Sarraf, Parsons; Benson Shing, ulated rural and desert areas. Fu- UCSD; Joséph Smith, Tobolski/Watkins; EQE (1988), The Superstition Hills ture earthquakes may shake more Andreas Stavridis, UCSD; Fred Turner, Earthquakes of November 23 & 24, densely populated areas, and could California Seismic Safety Commission; 1987, EQE Summary Report, 1988, cause more casualties, larger dam- Derrick Watkins, Tobolski/Watkins; and p.13. age, and much greater economic Richard Wood, UCSD. Munguia, L., Navarro, M., Valdez, T., losses. Most structures behaved as The GEER team: Jonathan Stewart, and Luna, M. (2010), Red de Acel- expected for the level of earthquake team leader, University of California, erografos del Noroeste de México intensity, exhibiting some damage Los Angeles (UCLA); David Ayres and (RANM): Preliminary report on the but not collapse. Nonetheless, the Scott J. Brandenberg, UCLA; John epicenter location and strong mo- damage indicates the need for Fletcher, Centro de Investigacion Cien- tion data recorded during the El attention in the following areas: tifica y de Educacion Superior de Ense- Mayor-Cucapah (Mw 7.2) earth- 1) improvement and development nada (CICESE); James R. Gingery, quake. CICESE, Ensenada, México. of low-cost foundation systems Kleinfelder; Tara Hutchinson, UCSD; Singh J.P. (1985), “Earthquake Ground for structures on liquefiable soil; Dong Youp Kwak, UCLA; Timothy P. Motions: Implications for Designing 2) seismic design of nonstructural McCrink, California Geological Survey; Structures and Reconciling Struc- Jorge F. Meneses, Kleinfelder; Diane components, particularly in hos- tural Damage,” Earthquake Spec- Murbach, Murbach Geotechnical; Thom- pitals and schools; tra, vol. 1, no. 3. as K. Rockwell, San Diego State Uni- 3) better seismic design of water versity; Orlando Teran, CICESE; and Steinbrugge, Karl (1940). Earth- and wastewater systems; and John C. Tinsley, US Geological Survey. quake Image Information Service, 4) better design of irrigation canals Earthquake Engineering Research in important agricultural regions Acknowledgments Center Online Archive. with high seismic risk. Earthquake reconnaissance offers great Ulrich, Franklin (1940). “The Imperial opportunities to develop and refine Valley Earthquakes of 1940,” Bul- current seismic design methodologies. letin of the Seismological Society of However, this work is challenging and America, V. 31, No. 1, pp. 13-31.