Ten years since 2004 Sumatera earthquake and three years since 2011 2011 Tohoku earthquake: Early-warning system alone cannot save everyone

Much  Japanese watched the tsunami video attacking  Banda Aceh on the 2004 Sumatra, and they have a lot of tsunami disaster memories, and early tsunami warming system. However,  we lost about  20,000 people by the 2011 Tohoku earthquake tsunami.  It makes clear that we never rescue the people from the tsunami only by an early warming syste. In February 2004, a research team of Nagoya University was coming to Banda Aceh to investigate the disaster on th 2004 Sumatra earthquake tsunami (I was a research member of Nagoya University  at the 2004 Sumatra earthquake, and joint the research team  since the first field survey in 2012). Not only the natural scientists but also the humanities’ scientists, including Indonesians join the research team, and field researches in Aceh have been continued every year until now. As results of the research, eight annual reports totally to 1,000 pages and four books, including writings in Indonesia are published. Through the first interviews in Banda Aceh, we understand that not so many peo- ple remained the tsunami coming after the earthquake felt, and when they watched the tsunami they never shouted ”Tsunami!”. They shouted out,”Sea is ascending”. As re- sults, there are many fatalities by the tsunami along the coastlines.They had no time to evacuate from the tsunami, because they started the evacuation after they watched the attacking tsunami. In one village, only the people going out the village to the down-town were saving their lives

Comparison of the Stochastic Models for Double-Differenced GPS Measurements

Double-differenced GPS carrier phase measurements are commonly used in GPS precise positioning applications and processed with algorithms based on the least-squares (LS) principle. In order to apply the LS principle, one needs to define properly both the functional and stochastic models. Whilst the functional model for precise GPS positioning is sufficiently well known, realistic stochastic modeling is still a difficult task to accomplish in practice. Incorrect stochastic models for double-differenced GPS measurements will lead to unreliable estimates for ambiguity resolution and, eventually, it will bias positioning results. The common assumption when we construct the stochastic model is that all raw GPS measurements are independent and have the same variances. In fact, this is not realistic, since due to varying noise levels measurements obtained from different GPS satellites cannot have the same accuracy. A realistic stochastic modeling should be able to capture the ordinary noises in the observables.In order to specify a realistic stochastic model for precise relative GPS positioning applications, in this paper the performance of three stochastic models namely the commonly used model or the standard model, the outer product of residual data vector model and Minimum Norm Quadratic Unbiased Estimation (MINQUE) are examined and effects of each the proposed model on statistic for ambiguity search and positioning accuracy are compared. The results indicate that the MINQUE model tends to perform better than the other models. Using the MINQUE model, the reliability of the ambiguity resolution and the statistics of the baseline components can be improved. It may suggest that the MINQUE model, which is based on modern statistical theory, is capable of capturing the ordinary noises

Isolating along-strike variations in the depth extent of shallow creep and fault locking on the northern Great Sumatran Fault

The Great Sumatran Fault system in Indonesia is a major right-lateral trench-parallel system that can be divided into several segments, most of which have ruptured within the last century. This study focuses on the northern portion of the fault system which contains a 200-km-long segment that has not experienced a major earthquake in at least 170 years. In 2005, we established the Aceh GPS Network for the Sumatran Fault System (AGNeSS) across this segment. AGNeSS observes large displacements which include significant postseismic deformation from recent large megathrust earthquakes as well as interseismic deformation due to continued elastic loading of both the megathrust and the strike slip system. We parameterize the displacements due to afterslip on the megathrust using a model based on a rate- and state-dependent friction formalism. Using this approach, we are able to separate afterslip from other contributions. We remove predicted deformation due to afterslip from the observations, and use these corrected time series to infer the depth of shallow aseismic creep and deeper locked segments for the Great Sumatran Fault. In the northern portion of this fault segment, we infer aseismic creep down to 7.3 ± 4.8 km depth at a rate of 2.0 ± 0.6 cm/year. In the southwestern portion of the segment, we estimate a locking depth of 14.8 ± 3.4 km with a downdip slip rate of 1.6 ± 0.6 cm/year. This portion of the fault is capable of producing a magnitude 7.0 earthquake

Karakteristik Deformasi Gunungapi Ijen dalam Periode 2002-2005 Hasil Estimasi Metode Survei GPS

Pemantauan aktivitas gunungapi dapat dilakukan dengan berbagai metode, dimana salah satunya adalah metode deformasi. Metode ini dapat diimplementasikan menggunakan beragam sensor dan teknik, dimana salah satunya adalah teknik yang menggunakan pengamatan terhadap satelit GPS (Global Positioning System). Makalah ini menjelaskan penggunaan metode survei GPS secara periodik untuk studi deformasi Gunungapi Ijen, gunungapi aktif tipe-A yang terletak di Jawa Timur. Dari hasil survei GPS yang telah dilaksanakan pada Juni 2002, April 2004, Juni 2004 dan Agustus 2005 teramati bahwa pada saat aktivitas gunung Ijen meningkat, pergeseran titik-titik pengamatan dapat mencapai sekitar 1-2 dm, baik dalam komponen horisontal maupun vertikal. Deformasi dalam level ini belum disertai dengan aktivitas letusan dari gunung Ijen

Comparison of the Stochastic Models for Double-Differenced GPS Measurements

Double-differenced GPS carrier phase measurements are commonly used in GPS precise positioning applications and processed with algorithms based on the least-squares (LS) principle. In order to apply the LS principle, one needs to define properly both the functional and stochastic models. Whilst the functional model for precise GPS positioning is sufficiently well known, realistic stochastic modeling is still a difficult task to accomplish in practice. Incorrect stochastic models for double-differenced GPS measurements will lead to unreliable estimates for ambiguity resolution and, eventually, it will bias positioning results. The common assumption when we construct the stochastic model is that all raw GPS measurements are independent and have the same variances. In fact, this is not realistic, since due to varying noise levels measurements obtained from different GPS satellites cannot have the same accuracy. A realistic stochastic modeling should be able to capture the ordinary noises in the observables. In order to specify a realistic stochastic model for precise relative GPS positioning applications, in this paper the performance of three stochastic models namely the commonly used model or the standard model, the outer product of residual data vector model and Minimum Norm Quadratic Unbiased Estimation (MINQUE) are examined and effects of each the proposed model on statistic for ambiguity search and positioning accuracy are compared. The results indicate that the MINQUE model tends to perform better than the other models. Using the MINQUE model, the reliability of the ambiguity resolution and the statistics of the baseline components can be improved. It may suggest that the MINQUE model, which is based on modern statistical theory, is capable of capturing the ordinary noises