Fakta : Gempa M9,0 yang berpusat di segmen Kepulauan Mentawai, Sumatra, terakhir terjadi pada 1883 silam, dengan rupture length 550 km dan total slip 13 m dengan estimasi kedalaman hiposentrum sekitar 10 - 20 km. Gempa ini menghasilkan emergence (pengangkatan) pada sejumlah pulau kecil di Kepulauan Mentawai sebagaimana terekam dalam terumbu-terumbu karang cincin (mikroatol) di pulau-pulau tersebut.
Dari pola-pola emergence dan submergence yang ada pada mikroatol ini, memang pak Danny Hilman N dan rekan-rekannya dari Caltech maupun Puslitbang Geoteknologi LIPI berhasil mendeduksi adanya siklus 200an tahun dalam perulangan gempa-gempa besar di segmen tersebut (ingat, hanya di segmen Mentawai) berdasarkan elastic dislocation modelling. Tepatnya siklus itu bernilai 230 tahun. Namun ketidakpastiannya masih sangat besar (mencapai 30-an tahun), karena interaksi antara lempeng Australia dan Sunda di bawah segmen Kepulauan Mentawai cukup kompleks seperti terlihat pada gempa ganda September 2007 silam. Hoax : Cerita soal gempa M 9,0 yang katanya bersumber dari CNN, itu hoax yang muncul sejak 2006 silam pasca gempa dan tsunami Jawa 17 Juli 2006. "Berita" itu kemudian diulang-ulang terus setiap tahun, hanya divariasikan dengan mengganti tanggal. Ini sama saja dengan hoax "Mars sebesar Bulan" yang muncul sejak Agustus 2004 dan selalu diulang-ulang terus setiap bulan Agustus. Mendeteksi hoax soal gempa mudah saja. Perkembangan ilmu seismologi dan earthquake geology sejauh ini baru bisa menghasilkan konklusi bahwa suatu daerah (misalnya segmen Kepulauan Mentawai) lebih berpotensi meletupkan gempa dengan perkiraan magnitude maksimum sekian skala Magnitudo. Potensi itu dinyatakan dalan probabilitas untuk jangka waktu tertentu (misalnya seperti di San Andreas Fault, yang secara rata-rata disebut akan mengalami gempa M 6,0 + pada kurun waktu 30 tahun mendatang dengan probabilitas 60 %). Jadi tidak meramalkan kedatangan gempa pada waktu yang eksak. Epilog : Ketimbang "meributkan" kapan gempa besar (M9,0 +) itu datang, pertanyaannya dibalik saja : sudah siapkah kita jika sewaktu-waktu gempa melanda tanah tempat kita tinggal dan berpijak? Sudahkah kita menyimpan surat-surat penting dalam satu tas? Sudahkah kita memiliki kotak P3K lengkap dengan senter? Sudahkah kita tahu bagian2 mana di kantor/rumah kita yang relatif lebih aman dari bahaya keruntuhan dibanding bagian yang lain? Sudahkah kita tahu ada beragam cara untuk menyelamatkan diri dari bahaya keruntuhan struktur bangunan akibat gempa, selain dengan melarikan diri ke tanah lapang? Menyiapkan hal-hal semacam itu jauh lebih berharga ketimbang main tebak-tebakan kapan gempa mengguncang. Salam, Ma'rufin ----- Original Message ---- From: Andya Primanda <[EMAIL PROTECTED]> To: [EMAIL PROTECTED] Sent: Monday, September 15, 2008 11:33:51 PM Subject: [sains] Fw: [bio-ui] artikel asli gempa 17 september Ada kakak kelas saya yg bersusah payah nyariin artikel asli "gempa 17 september", dan ternyata ketahuan bahwa beritanya ...kadaluarsa. 17 September 2007. All day long he was fighting for you And he didn't even know your name --Phil Collins, "That's Just The Way It Is" --- On Tue, 16/9/08, safran yusri <safran_yusri2003@ yahoo.com> wrote: From: safran yusri <safran_yusri2003@ yahoo.com> Subject: [bio-ui] artikel asli gempa 17 september To: "milis bio ui" <[EMAIL PROTECTED] com> Date: Tuesday, 16 September, 2008, 11:51 AM Imel tentang gempa ini hoax (imel palsu) atau penulis email salah mengartikan artikel dari cnn. Inti dari artikel adalah Indonesia memang dalam ancaman, oleh sebab itu harus bersiap-siap. Tetapi gempa tidak diketahui kapan akan terjadi. tanggal 17 september ternyata tanggal publikasi (17-09-2007) . Artikel ini sudah setahun. tolong teman-teman yang keburu forward imel sebelumnya juga bertanggung jawab untuk mengklarifikasi berita ini Artikel asli: sumber: http://edition. cnn.com/2007/ WORLD/asiapcf/ 09/17/indonesia. quake/index. html Indonesia's big one 'on its way' By Hugh Riminton CNN PADANG, Indonesia (CNN) -- An international team of earthquake specialists says Indonesia faces another potential "giant" quake in the near future. A worker constructs a wall to protect against tsunami waves in Lais, North Bengkulu, Saturday. 1 of 2 more photos ยป var CNN_ArticleChanger = new CNN_imageChanger( 'cnnImgChngr' ,'/2007/WORLD/ asiapcf/09/ 17/indonesia. quake/imgChng/ p1-0.init. exclude.html' ,1,1); //CNN.imageChanger. load('cnnImgChng r','imgChng/ p1-0.exclude. html'); The scientists, including a team from the California Institute of Technology, says three major quakes in the last week have increased the likelihood of a major disaster. CNN traveled to the earthquake zone with a scientist who deliberately puts himself in the path of the world's most powerful quakes. Smack on the equator, Indonesia's Sumatra island holds the deadliest stretch of ocean in the world. "You'd see a strip 30 meters high, stripped down to bedrock," says John Galetzka, a former U.S. Army ranger who is now adventuring on another frontline as an earthquake geologist. He is investigating the fault line that sparked the 2004 tsunami and, in recent days, three more powerful quakes. Last Friday, Galetzka shot video footage of the shaking beach, with startled locals scrambling upshore. His thoughts turned immediately to the tsunami danger, and his command ship offshore. Just moments later he caught the panic near the beach, as he saw families evacuating to the hills about 200 meters behind their village. The day before, another big quake struck -- larger, but further away. Galetzka recalls the long slow waves and a shivering water bottle. For the American geologist, this is where theory meets reality. "I just felt like the luckiest man alive to feel two strong events," he says. "You can almost hear the excitement in my voice -- oh my gosh, this is it, this is it ..." Galetzka is now examining the evidence that his team believes indicates the arrival another giant earthquake, and possible tsunami. He has established a network of position-markers, linked by satellite, that show a constant creep, northeast, among the islands on Indonesia's Indian Ocean frontier. The first one was placed in August 2002. The 30 measuring stations along Sumatra's western coast tell an ominous tale. Driven by the plate beneath the Indian Ocean, the entire coastline is flexing, as the earth literally bends. The pressures are already enormous, and at some point probably soon, they will become intolerable. The implications are terrifying. "Eventually it has got to release in (the form) of giant earthquake," states Galetzka matter-of-factly. It could be a rare magnitude-9 quake, and with the plates so tightly sprung, it will happen sooner, he believes, rather than later. Knowing what he knows, does he worry about the people living along this coast? "I absolutely do," he replies. "I tell them to be prepared. Whenever I am in Padang I think about my escape routes, almost every moment." As he criss-crosses around the islands, searching for data, Galetzka says his aim is to save lives. But he, more than anyone, knows the risks -- that one day he'll confront a giant wave, a tsunami powerful enough to swallow islands. The geologist's voice quivers as he imagines "the big one." "If we saw it, we'd just head right into it. I'd shake your hand and say, good luck!" Safran Yusri
