Mengenang Tsunami Jepang 2011

Hari itu mendapatkan email dari salah satu penasihat komunikasi GNS untuk menulis di media. Sebentar lagi peringatan 10 tahun tsunami Jepang yang menyebabkan kerugian material dan korban jiwa yang terbesar dalam sejarah Jepang. Science Magazine akan mengeluarkan review tentang kejadian tersebut yang ditulis oleh peneliti dari Jepang. New Zealand memiliki Science Media Centre yang secara rutin menerbitkan tanggapan oleh para ahli tentang suatu temuan atau kebijakan penting.

Baru saja terjadi tiga tsunami di New Zealand. Dan saya sedang tidak kekurangan pekerjaan. Rasanya ingin sekali menolak menulis karena hanya akan menambah pekerjaan. Tetapi secara moral seharusnya saya melakukan sesuatu untuk mengenang tsunami tersebut. Lagi pula sepertinya di GNS tidak ada orang yang lebih tepat lagi mereview kejadian tsunami di Jepang selain saya.

Paper Science tersebut akhirnya saya baca. Baru membaca paragraf ternyata banyak hal yang dahulu pernah saya pelajari kembali lagi. Waktu di Jepang tidak sedikit melihat presentasi tentang riset tsunami Tohoku 2011. Setelah membaca sekali, sepertinya sudah siap untuk membuat draft review. Rerview saya tulis perlahan dengan beberapa kali membaca ulang apa yang ada di Paper. Dikepala ini seperti memainkan informasi yang dulu pernah diterima dengan informasi dari paper.

Akhirnya orderan si penasihat tadi untuk menghasilkan tulisan dalam beberapa jam saja saya penuhi. Ngordernya sore, harus jadi besok paginya. Serasa mahasiswa lagi. Besoknya si John datang kekantor untuk lebih lanjut ngobrol-ngobrol tentang pengalaman saya ketika kejadian. Pada saat gempa saya sedang menghadiri seminar tentang tsunami Aceh 2004 di Kampus Kashiwa Tokyo Daigaku. Dan ternyata bukti fotonya ada.

May be an image of 23 people, including Udrekh Hanif and Rahma Hanifa and people standing
Foto bersama peserta seminar setelah merasakan guncangan dari gempa Tohoku 2011 di kampus Universitas Tokyo di Kashiwa. Foto ini di dapat dari halaman facebooknya Rahma Hanifa (peneliti Indonesia berjilbab yang ada di foto).

Judul paper yang Science yang dimaksud berjudul

Investigating a tsunamigenic megathrust earthquake in the Japan Trench

Komentar yang saya berikan untuk paper tentang tsunami Tohoku yang dipublikasi di sini adalah sebagai berikut:

Dr Aditya Gusman, Tsunami Modeller, GNS Science, comments:

“At the time of this event I was at a conference on the 2004 Indian Ocean earthquake and tsunami at The University of Tokyo, some 500km from the quake epicentre. Once the strongest shaking stopped – during which it was difficult to stand up – we evacuated the building. Highrise buildings everywhere were swaying markedly. Strong aftershocks continued for days. Trains stopped shortly after the earthquake and many people had to walk home. Some stayed at train stations because it was too far to walk. Supermarkets gave out emergency supplies such as blankets, water, and food for those unable to go home.

“This paper reviews the main findings from investigations following the 2011 Tōhoku earthquake. The event produced huge datasets that can be used to better understand the Japan subduction zone. The rich datasets are the result of Japan’s dense networks of seismic, geodetic and tsunami instruments.

“Large tsunamis were known to have occurred in the past from earthquakes in the Japan trench from historical records as well as geological evidence of tsunami deposits along Japan’s east coast. The 2011 Tōhoku tsunami runups reached a maximum of 40m, and were higher than 20m along 200km of Tōhoku coast.

“The large tsunami was estimated to have been caused by the large fault slip near the trench. Horizontal slip displacements of more than 30m were recorded at underwater geodetic stations.

“Scientific drilling into the rupture zone near the trench revealed that the plate boundary was confined by a layer of pelagic clay. The weakness of this clay layer may help to explain the very large slip. The probability of another M9 earthquake soon in this region is low.

“However, the stress state after the 2011 Tōhoku thrust earthquake might bring other types of tsunamigenic earthquakes closer to rupture. The earthquake has already been followed by one normal-faulting event that generated small tsunami.”

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