Precursory Crustal Movements Associated with Major Earthquakes

Abstract

A history of anomolous crustal motion precedes major earthquakes. Crustal movements prior to the Kanto (1930; M = 6.9), Nigate (1964; M = 7.0) and Izu-Oshima (1978; M = 6.8) earthquakes in Japan and the Tangshan (1976; M = 7.8), Haicheng (1976; M = 8.0) and Songpan (1976; M = 7.2) erathquakes in China are only a few examples. Similar movements have also been reported in Southern California. Experimental studies suggest rock deformation under simulated crustal conditions produces a combination of elastic and inelastic volume dilatancy. Field evidence for gravity decrease, water expulsion and radon emission in seismic regions suggests a mode of volume dilatancy occur during precursory stages of major earthquakes. Preseismic crustal movements can therefore be interpreted as surficial expressions of volume dilatancy at subcrustal levels in a 'slip-deficient seismic zone.

Keywords

• Earthquake
• Precursor Crustal Movements
• Seismic

Büyük Depremlerle İlişkili Öncül Kabuk Hareketleri

Abstract

Büyük depremler öncesi anormal kabuk hareketlerinin var olduğu bilinmektedir. Japonya’daki Kanto (1930; M=6.9), Niigate (1964; M=7.0), İzo-Oshima (1978, M=6.8), Çindeki Tangshan (1976, M=7.8), Haicheng (1976; M=8) ve Songpan (1976; M=7.2) depremleri öncesi görülen kabuk hareketleri bunların güzel örneklerinden birkaçıdır. Benzer hareketler Güney Kaliforniyada da gözlenmiştir. Deneysel çalışmalar, kayaların deformasyon etkisiyle elastik ve elastik olmayan hacim büyümesine maruz kaldıklarını göstermiştir. Sismik bölgelerde gözlenen gravite azalması, kaynak su boşalımları ve radon gazı kaçaklarındaki artışlarda kayaların bir tür hacim büyümesine uğradıklarını göstermektedir. Bu nedenle öncül kabuk hareketleri kayalardaki hacim büyümesinin yüzeysel ifadesi olarak değerlendirilebilirler.

Keywords

• Deprem
• Öncül Kabuk Hareketleri
• Sismik

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