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A4-001
16:10
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16:30
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THE FORMATION AND FAILURE OF LANDSLIDE DAM IN CHICHI EARTHQUAKE 1999 AND TYPHOON MORAKOT 2009
Landslide dams have proved to be both interesting natural phenomena significant hazards in many areas of the world. A few of these blockages attain heights and volumes that rival or exceed the world’s largest man-made dams. Because landslide dams are natural phenomena and thus are not subject to engineering design (although engineering methods can be utilized to alter their geometries or to add physical control measures), they are vulnerable to catastrophic failure by overtopping and beaching. Some of the world’s largest and most catastrophic floods have occurred because of failure of these natural dams. Most landslide dams are remarkably short-lived. Overtopping was by far the most frequent cause of landslide-dam failure. The timing of dam failure and the magnitude of the resulting floods are controlled by dam sizes and geometry; material characteristics of the blockage; rate of inflow to the impoundment; size and depth of the impoundment; bedrock control of flow; and engineering controls, such as artificial spillways, diversions, and blasting. The Chichi earthquake 1999 and Typhoon Morakot 2009 scarred the Taiwan landscape and caused over ten landslide dams, respectively. Natural dams may cause upstream flooding as the lake rises and downstream flooding as a result of failure of the dam. For the purpose, the study collected and analyzed the numerous kinds of natural dams from field survey. Finally, landslide dams can be classified into five categories and some methods of disaster mitigation.
Su-Chin Chen
breach, CHICHI EARTHQUAKE, landslide dam, overtopping, Typhoon Morakot.
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A4-011
16:30
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16:45
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CAN WE UNDERSTAND LANDSLIDE FROM COSEISMIC LANDSLIDE SEISMIC SIGNALS?
Understanding the landslide with seismology has been well established in the past decade. Most of studies demonstrated that the landslide-induced seismic signals could be used to extract the source parameters, including runout path, size, sliding velocity of landslide source. However, the seismic signals generated by coseismic landslide generally embedded in the signals induced by earthquake. A scheme of signal identification is needed to isolate the signals from coseismic landslide and earthquake. The procedure of identification of coseismic landslide seismic signal (ICOL) was developed in our study, which can identify coseismic landslide signals based on 1) the seismic radiation pattern, 2) the synthetic waveform modeling, the time-frequency analysis and the amplitude tracing method (ATM). We then applied the ICOL approach to study the coseismic landslides and further extract the source parameters such as centroid time and sliding direction of landslide, by using the coseismic landslide signals. The events used in this study are Tsaoling landslide, Daguangbao landslide and Japan landslide triggered by the 1999 Mw7.6 Chi-Chi earthquake, the 2008 Mw7.8 Wenchuan earthquake and the 2008 Mw7.2 Iwate-Miyagi earthquake, respectively. Our resulting demonstrates that the detection of coseismic landslide signals is possibly using a combination analysis of the ICOL and Newmark-based scheme.
Che-Ming Yang, Yi-Han Wu, vvn Weian Chao
amplitude tracing method (ATM), Chi-Chi earthquake, identification of coseismic landslide (ICOL), Newmark method, seismic signal
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SS1-011
16:45
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17:00
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LOWER-CRUSTAL RHEOLOGY IN THE TAIWAN OROGEN REVEALED BY THE POSTSEISMIC TRANSIENTS FOLLOWING THE 1999 CHI-CHI EARTHQUAKE
Geodetic measurements in Taiwan indicate that a short-term rapid deformation followed by a prolonged period of slow deformation occurred after the 1999 M w 7.6 Chi-Chi earthquake. Such a transient deformation is so-called “postseismic deformation”, a response of the lithosphere to its internal stress relaxation. The mechanisms involved in postseismic deformation include long-lasting distributed viscoelastic flow and localized afterslip on faults surrounding the epicenter. Therefore, the continuous observations of surface postseismic displacements over a decade with a dense GPS network following the Chi-Chi earthquake allow us to investigate the rheology of the deep crust with a decent spatial and temporal resolution. We constrain the rheological properties beneath the Taiwan orogenic belt using the stress perturbation following the Chi-Chi mainshock and 14 years of geodetic observations after the earthquake. We invert the strain/strain-rate evolution in the lower crust and eliminate the effect of localized afterslip by formulating a joint inversion for fault slip and viscoelastic flow. We demonstrate that the evolution of strain-rate in the lower crust is best explained by a power-law Burgers rheology, suggesting that rocks exhibit nonlinear transient creep shortly after the mainshock before reaching steady-state dislocation creep. This rheological feature is in accordance with the observations of seismic anisotropy in the Taiwan orogen. Our analysis indicates that lower-crustal rocks strengthen rapidly from effective viscosities as low as 10 17 Pa s to 10 19 Pa s within a year, and to 2×10 19 Pa s over a decade. By incorporating the laboratory-derived flow laws for felsic rocks and their associated uncertainties, we estimate the thermal gradients increase from 17-22 ºC/km in the Coastal Plain to 29-35 °C/km in the Central Range. Our study demonstrates the potential for geodetic observations to investigate lower-crustal rheology and its implication for tectonic evolution, bridging the gap between laboratory and lithospheric scales.
Wu-Lung Chang, Chi-Hsien Tang, Ya-Ju Hsu, Sylvain Barbot, James D. P. Moore
1999 Chi-Chi Earthquake, earthquake cycle, postseismic deformation, rheology
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B7-012
17:00
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17:15
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TEMPORAL VELOCITY CHANGES IN THE CRUST OVER 2005?2015 NEAR THE SUMATRA SUBDUTION ZONE EXAMINED USING REPEATING AFTERSHOCKS
Long-term monitoring temporal changes in the crust is important for understanding the co- and post- seismic processes of an earthquake. We have examined temporal velocity changes induced by the 2004 Mw 9.2 Sumatra?Andaman and the 2005 Mw 8.6 Nias?Simeulue great earthquakes over 2005?2008 using repeating aftershocks (RA). Here we expand our analyses of RA and temporal velocity changes over 2005?2015, and for the Bengkulu?Mentawai segment. For the RA near Banda Aceh and the Nias island, those RA continue to occur to the end of 2015. For the RA near the Bengkulu?Mentawai segment, their occurrence is primarily activated by the 2007 September Mw 8.4, Mw 7.9, and Mw 7.0 Bengkulu earthquake sequence. Seismic observations exhibit the following patterns: (1) velocity of high frequency S coda waves, denoted as δVS, continues to increase over time since 2004 and 2005 main shocks, with a total amount of ~0.1% over 2005?2015; and (2) for long period Rayleigh wave phase velocity, denoted as δVLR, the 2007 Bengkulu earthquake sequence interrupt velocity recovery of δVLR and produce a reduction of about ?0.4% for the RA near Banda Aceh and Nias as well as the Bengkulu regions; the magnitude of reduction of δVLR induced by the 2007 Bengkulu earthquake sequence is larger than that induced by the preceding 2004 and 2005 main shocks by a factor 2?4 for the RA near Banda Aceh and Nias. Temporal recovery of δVS is compatible with post-seismic afterslip of earthquakes at depth, whereas δVLR would reflect healing of the near-surface structures induced by strong ground motion of earthquakes, and the subsequent velocity drop reflects re-damage induced by the 2007 Bengkulu earthquake.
W. Yu, J.T. Lin, J. Su, T.R.A. Song, C.C. Kang
2007 Bengkulu Earthquake, seismology, re-damage
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B7-014
17:15
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17:30
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EVALUATING THE ASSOCIATION BETWEEN TECTONIC TREMORS AND EARTHQUAKES IN TAIWAN FROM SEVEN YEARS CATALOGS
Knowledge of what governs the interaction between slow- and fast-slip earthquakes is essential to understanding the nature of the earthquake cycle. In southern Taiwan, four major earthquakes (2008 Mw 5.2 Taoyuan, 2010 Mw 6.4 Jiashian, 2012 Mw 5.9 Wutai, and 2016 Mw 6.4 Meinong events) that occurred near the active tremor areas provide a unique opportunity to analyze their spatiotemporal association. With the declustered tremor catalog built in this study, we were able to statistically evaluate the possible association between tremor and mainshock-aftershock sequences in space and time. We found close-by mainshocks influences tremor’s timing in a matter of less than 5 days by short-term triggering, while the 2010 ML 6.4 Jiashian earthquake appears to be most responsible for such triggering. Assuming a low dip-angle thrust faulting mechanism, tremors coincided with small static stress increases (8 kPa) in the 2010 ML 6.4 Jiashian earthquake. The other three major events, however, caused either negative or neglectable stress changes in the tremor zone. The different responses of the tremors can be explained by coseismic slip-induced static stress change. In this complex tectonic region as a boundary between continental subduction and collision, the interaction between slow- and fast-slip phenomena could be facilitated by a commonly high fluid pressure environment.
Shinji Toda, Kate Huihsuan Chen, Wei Peng
short-term triggering, static stress change, tremor
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B7-013
17:30
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17:45
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Scattering and intrinsic attenuation of S-waves in the southern Aegean derived using Multiple Lapse Time Window analysis
Southern Aegean is characterized by an ongoing process of oceanic subduction. In this study, shallow depth (< 40 km) events recorded by temporary and permanent seismic networks in southern Aegean are used to study the scattering attenuation (Qs-1) and intrinsic attenuation (Qi-1) of S-waves. The 3 component S-waveforms are filtered in 2-4, 4-8, 8-16 and 16-32 Hz bands and envelopes are calculated as root mean square of individual components. The Multiple Lapse Time Window (MLTW) analysis is separately applied for each station in 3 time windows: from S onset to 15 s after, 15 s to 30 s after and 30 s to 45 s after the S onset. Coda normalization is used to remove the effects of source spectrum and site amplification. The integral of envelopes in each of the 3 time windows are modeled using the time dependent solution of Boltzamann equation in 3 dimensional media. The fitting is performed using Levenberg-Marquardt algorithm which is a non-linear least squares method. The results obtained for each station are interpolated using delaunay triangulation grid. The final results indicate high Qs-1 along the volcanic arc and back-arc while low Qs-1 in the fore-arc. Also, an increasing trend of Qs-1 is observed as we move from south to north. High Qi-1 is also observed along the volcanic arc. These results are consistent with the geodynamics of southern Aegean subduction zone. Our study provides useful insight about the attenuation in the southern Aegean crust which has implications for ground motion and seismic hazard in this region.
Pratul Ranjan, Kostas Konstantinou
attenuation, intrinsic, Multiple Lapse Time Window, scattering, southern Aegean
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B6-013
17:45
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18:00
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Single-Station Classification of Tectonic Tremor Using Fisher’s Class Separability Criterion-Based Feature Selection
The detection of tectonic tremor relies heavily on the similarity and time lapse of the arrival of tremor bursts from multiple stations. Here we explore the possibility of classifying minute-long tremor using a single station classification method. This method bases on the k-nearest neighbor (k-NN) classifier and Fisher’s class separability criterion to distinguish tremor from earthquakes and noise. During the study period of January 1 to September 16, 2016 when a local seismic array was deployed, we successfully differentiated tremor from local earthquakes and noise with a higher than 92.1 % accuracy averaged over three stations using 612 training data sets for each station. The classification accuracy is improved to 95.6 % with feature extraction using Fisher’s score, suggesting that a single-station classifier is applicable for future tremor monitoring systems.
Ting-Chen Yeh
machine learning, tremor
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