Cika wannan jumla: A ilimin kasa, girgizar kasa ta El Centro ta 1940 a kan sikelin Mercalli. Wannan ita ce girgizar ƙasa ta farko da aka yi rikodin ta wurin na'urar da ake kira seismograph da ke kusa da wani wurin da girgizar ƙasa ta yi ɓarna. An yi nazari sosai ta hanyar injiniyoyi na gine-gine kuma an ɗauka cewa yana da kyau har sai da aka gina gine-ginen gine-ginen gine-gine.
Girgizar kasa ta Northridge a shekara ta 1994. A cikin wannan yanki, ilimin geology ya mamaye sauyin iyakar tectonic plate daga rift zuwa transverse fault. Yankunan kudancin San Andreas Fault suna haɗuwa da mafi girman arewacin Gabashin Pacific Rise. Sakamakon haka, yankin yana fuskantar girgizar ƙasa, kuma ana shimfiɗa farfajiyar ƙasa, wanda hakan ke haifar da nutsewar ƙasa a cikin lokaci.