HUBUNGAN ANTARA SIFAT-SIFAT FISIKA BATUAN
5. Perubahan parameter fisis terkait dengan proses perusakan
Perusakan berhubungan dengan perubahan keadaan internal batuan. Perubahan
pre dan post perusakan adalah subjek studi tentang proses perusakan dan masalah
prediksi gempabumi. Volarovich dan Budnikov (1979) telah menyelidiki perubahan kecepatan gelombang P dan S selama dilakukan eksperimen tekanan uniaksial pada plagiogranit dan genis. Kecepatan yang didapat dari observasi ditunjukkan pada gambar 4.11 dalam grafik vp/vs vs vs.
Gambar 4.11 Analisa perubahan rasio vp/vs selama proses perusakan
Grid: perhitungan model dengan struktur internal untuk sudut struktur yang berbeda-beda () dan parameter pertalian (f); faktor empiris A adalah 7800 m/s
Titik: data eksperimen (dari Volarovich dan Budnikov, 1979); anak panah menunjukkan arah kenaikan tekanan (dari 0 sampai sekitar 0.8 Gpa pada saat terjadi perusakan)
o adalah plagiogranit dan
67 Pada fase pre-perusakan data mengikuti loop perubahan struktur dan pertalian yang dominan. Perubahan struktur mungkin adalah perubahan pada sistem perusakan aktif arah utama dibawah kondisi 3 tekanan. Perubahan pertalian dengan naiknya nilai parameter f dapat diinterpretasikan sebagai hilangnya hubungan mekanik antara butir dan mineral disepanjang retakan dan kerusakan lainnya. Fenomena ini mungkin berhubungan dengan dilatasi. Contoh ini menunjukkan bahwa konsep sebuah model termasuk struktur dan pertalian mungkin cocok untuk menganalisa fenomena kerusakan.
Gambar 4.12. Perubahan kecepatan gelombang longitudinal dan transversal pada lempeng tektonik aktif daerah California. Data dari Aggarwal et al. (1973)
a) data vp dan vs observasi dan rasio; anak panah menunjukkan kejadian dengan magnitudo M>4 b) hasil perhitungan vp/vs vs vs dan data observasi dari gambar 10.27a (hanya 2 loop yang diplot), A
68 Penelitian seismologi untuk gelombang longitudinal dan transversal (Gambar 4.12a) lebih dari periode 11 tahun ditunjukkan pada grafik vp/vs vs vs (gambar 4.12b dan 4.12c). Juga ditunjukkan tipikal-tipikal loop gempabumi. Loop yang lebih kecil berhubungan dengan magnitudo yang kecil pada tahun 1964 dan loop yang besar berhubungan dengan gempabumi San Fernando pada tahun 1971.
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