In early 1971 , the San Fernando Valley was the scene of a dense network of strong-motion seismometers , which provided a total of 241 seismograms . This made the earthquake the most documented event , at the time , in terms of strong-motion seismology ; by comparison , the 1964 Alaska earthquake did not provide any strong motion records . Part of the reason there were so many stations to capture the event was a 1965 ordinance that required newly constructed buildings in Beverly Hills and Los Angeles over six stories in height to be outfitted with three of the instruments . This stipulation ultimately found its way into the Uniform Building Code as an appendix several years later . One hundred seventy-five of the recordings came from these buildings , another 30 were on hydraulic structures , and the remainder were from ground-based installations near faults , including an array of the units across the San Andreas Fault
1964 Alaska earthquake
1964 Alaska earthquake
1971 San Fernando earthquake