Jerin girgizar ƙasa a California

Girgizar ƙasa ta farko da aka sani a jihar California ta Amurka an rubuta ta ne a cikin 1769 ta hanyar masu binciken Mutanen Espanya da mishaneri na Katolika na balaguron Portolá yayin da suke tafiya zuwa arewa daga San Diego tare da Kogin Santa Ana kusa da shafin Los Angeles na yanzu. Shugabannin jiragen ruwa da sauran masu bincike sun kuma rubuta girgizar kasa. Kamar yadda aka gina Ayyukan Mutanen Espanya tun daga ƙarshen karni na 18, an adana bayanan girgizar ƙasa. Bayan an lalata ayyukan a cikin 1834, rubuce-rubuce sun kasance kaɗan har zuwa lokacin da aka fara samun zinariya a California a cikin shekarun 1840. Daga 1850 zuwa 2004, akwai game da wani abu mai yuwuwa a kowace shekara a matsakaici, kodayake da yawa daga cikin waɗannan ba su haifar da mummunan sakamako ko asarar rai ba.

Tun da girgizar asa guda uku da ta faru a tsakiyar Yammacin Amurka da Gabas ta Gabas ta Amurka (1755 Cape Ann, 1811-1812 New Madrid, 1886 Charleston) sun kasance sananne, ya bayyana ga mazauna cewa haɗarin girgizar ƙasa ya bambanta a California.  Yayin da 1812 San Juan Capistrano, 1857 Fort Tejon, da 1872 Owens Valley girgiza sun kasance a mafi yawan yankunan da ba a cika su ba kuma kawai suna da lalacewa, abin da ya faru na Hayward na 1868 ya shafi tattalin arziki na San Francisco Bay Area, tare da lalacewa daga Santa Rosa a arewa zuwa Santa Cruz a kudu.  A wannan lokacin, masana kimiyya sun san wannan barazanar da kyau, amma ilimin kimiyyar ƙasa yana cikin ƙuruciya.  Biyo bayan girgizar ƙasa mai lalacewa a ƙarshen 19th da farkon ƙarni na 20, masu haɓaka gidaje, latsawa, da masu haɓakawa sun rage tare da rage haɗarin girgizar ƙasa saboda fargabar cewa haɓakar tattalin arziƙin da ke gudana za a yi mummunan tasiri.

A cewar masanin girgizar kasa Charles Richter, girgizar kasa ta San Francisco ta 1906 ta sa gwamnatin Amurka ta amince da matsalar.  Kafin wannan, babu wata hukuma da ta mayar da hankali musamman kan binciken ayyukan girgizar kasa.  Ofishin Yanayi na Amurka ya yi rikodin lokacin da suka faru kuma wasu masana kimiyyar binciken ƙasa na Amurka sun ɗan yi watsi da ayyukansu na yau da kullun na taswirar albarkatun ma'adinai don rubuta rahotanni game da abubuwan da suka faru na New Madrid da Charleston, amma babu wani ƙwararrun masanin ilimin ƙasa da ke aiki akan matsalar har sai bayan 1906 lokacin da Amurka Coast Coast da Geodetic Survey aka sanya alhakin.  Hankalin ya inganta lokacin da Farfesa Andrew Lawson ya kawo shirin sa ido na farko na jihar a kan layi a Jami'ar California, Berkeley a cikin 1910 tare da masanin kimiyyar girgizar kasa Harry Wood, wanda daga baya ya taka rawa wajen samun dakin gwaje-gwaje na Seismological Caltech a Pasadena a cikin 1920s..

Abubuwan da suka faru na farko a dakin gwaje-gwaje na Caltech sun haɗa da cibiyar lura da girgizar ƙasa ta amfani da ma'aunin girgizar kasa na ɗan gajeren lokaci, sikelin Richter, da sikelin ƙarfin Mercalli mai canzawa (wani sabuntawa na sikelin ƙarfin mercalli). A cikin 1933, Girgizar kasa ta Long Beach ta faru a cikin wani yanki mai yawan jama'a kuma ta lalata ko lalata gine-ginen makarantun jama'a da yawa a Long Beach da Los Angeles. Bayan 'yan shekarun da suka gabata, Girgizar kasa ta San Fernando ta shafi Kwarin San Fernando a arewacin Los Angeles tare da mummunar lalacewa ga asibitoci da yawa. A lokuta biyu, ra'ayi na masu tsara manufofin California ya canza, kuma an canza dokokin jihohi da lambobin gini (tare da muhawara mai yawa) don buƙatar gina kadarorin kasuwanci da na zama don tsayayya da girgizar ƙasa. An kafa ka'idoji mafi girma don tashoshin wuta, asibitoci, da makarantu, kuma an ƙuntata gina gidaje kusa da kuskuren aiki.

## Yanayin tectonic
A cikin Shekaru miliyan 66 da suka gabata, kusan dukkanin gabar yammacin Arewacin Amurka sun mamaye yankin subduction, tare da farantin Farallon da ke ƙarƙashin Farantin Arewacin Amurka. A halin yanzu, farantin Juan de Fuca (tare da farantin tauraron dan adam na Explorer da Gorda) da farantin Rivera da Cocos sune kawai ragowar farantin Farallon da ya Mai Girma. Yankin farantin da ya kasance a California shine na San Andreas Fault (SAF), iyakar farantin Pacific-North American wanda ya kai gabas zuwa Lardin Basin da Range na gabashin California da yammacin Nevada (wani yanki mai aiki da girgizar ƙasa da ake kira Walker Lane) da kudu maso yamma zuwa yankin California Continental Borderland daga tsakiyar da kudancin gabar teku. Wannan tsarin kuskuren ya ƙare a arewa a mahaɗar uku ta Mendocino, ɗaya daga cikin yankuna masu yawan girgizar ƙasa a cikin jihar, inda girgizar kasa a wasu lokuta sakamakon lalacewar intraplate ne a cikin farantin Gorda. Ya ƙare a kudu a Tekun Salton inda motsi ya sauya zuwa jerin Cibiyoyin yadawa da canza kuskuren, farawa da yankin Brawley a cikin kwarin Imperial.

A cikin Yankin San Francisco Bay, tsarin laifuffuka na San Andreas ya ta'allaka ne a cikin teku da kuma yankin Gabashin Bay, tare da mafi yawan laifuffukan suna kwance a gabas na babban laifin San Andreas (SAF).  Akwai yuwuwar kashi 70 cikin ɗari cewa ɗaya daga cikin waɗannan kurakuran zai haifar da girgizar ƙasa mai karfin Mw 6.7 ko mafi girma kafin 2030, gami da yankin Hayward Fault Zone, wanda ya wuce matsakaicin lokacin dawowar sa na shekaru 130 (shekaru 156 da suka gabata kamar na Agusta 2025).  Yayin da SAF ke da shiru a arewacin San Francisco, sashin tsakiya na SAF kusa da San Juan Bautista shine inda aka fara nazarin raƙuman ruwa, kuma a kudu shine inda girgizar ƙasa ta Parkfield ke faruwa.  Laifi na biyu sun kasance zuwa yamma na babban SAF a matsanancin yanki na kudu, gami da yankin San Jacinto Fault mai aiki da matasa, wanda maiyuwa ne zai mamaye a matsayin babban kan iyaka kudu da Cajon Pass.  Wani bincike na paleoseismic ta amfani da Lidar ya nuna cewa sama da ƙafa 16 (5 m) na zamewa sun taru tun a shekarar 1857 a kudancin SAF, wanda ke iyaka da Hamadar Mojave zuwa arewa da gabas na Babban Yankin Los Angeles.  Kusa da Matsakaicin Matsakaicin, kurakuran juyawa da tuƙi sun haifar da girgizar ƙasa mai lahani a Santa Barbara da Kwarin San Fernando..

## Girgizar ƙasa da aka sani