 The Imperial County Services building , a six @-@ story reinforced concrete building located 29 km ( 18 mi ) northwest of the epicenter in El Centro , was built in 1971 when there were few other tall buildings in the area . The decision to equip the building with nine strong motion sensors in May 1976 was based on its size , structural attributes , and location in a seismically active area . Unusually detailed structural analysis was possible as a result of the building having been outfitted with the instrumentation . The initial configuration was tested shortly after its installation when a relatively small ( 4 @.@ 9 local magnitude ) earthquake occurred 32 km ( 20 mi ) northwest of the building on November 4 , 1976 . The accelerations recorded on the equipment during the event proved to be of very low amplitude and , as a result , the instrumentation was upgraded to include a 13 channel configuration in the building along with a Kinemetrics triaxial ( 3 channel ) accelerograph located 340 ft ( 100 m ) east of the building at ground level . The full 16 channel system was managed by the California Division of Mines and Geology Office of Ground Motion Studies and provided almost 60 seconds worth of high resolution data during the 1979 event . 
