||A Statistical Model for the Impact of the 1999 Chi-Chi Earthquake on the Subsequent Rainfall-induced Landslides
||Department of Earth Sciences
A statistical model is proposed for the temporal influence of the 1999 Chi-Chi earthquake on the subsequent rainfall-induced new landslides in the Jhuoshuei River Watershed of Central Taiwan. Based on the landslide inventory via satellite image classifications and daily precipitation records from 1996 to 2008, the parameters of the model functions were obtained by genetic algorithm. The proposed model gives estimation from daily precipitation with an average error of 13.91% of new landslide density to the variation analysis result from landslide inventory over 15 image dates. The results of the model estimation reveal a continuously decaying pattern of earthquake influence on the subsequent rainfall-induced new landslides, an average daily 0.004‰ background new-landslide density, and a 4.97‰ new-landslide density caused by the earthquake directly within the study area. Also, the estimations of the models suggest that there are influences and latency of antecedent rainfall among the occurrence of new landslides.
Estimations from time-decay earthquake-impact-factor models show consistent results on the decay constant of 0.0012, which is equivalent to a 578-day (1.58-year) half-life for the influence of an earthquake. Model validations show more representative estimations on short-term (i.e., days) precipitation records and decreasing function for the impact factor of antecedent rainfall. However, constant-impact model of antecedent rainfall is recommended if there is no sufficient observations.
TABLE OF CONTENTS IV
LIST OF TABLES VI
LIST OF FIGURES VII
CHAPTER ONE INTRODUCTION 1
1.1 Landslides 1
1.2 Geologic Background of Jhuoshuei River Watershed. 2
1.3 The Chi-Chi earthquake 4
1.4 Thesis Overview 4
CHAPTER TWO LITERATURE REVIEW 6
2.1 Landslide Triggers. 6
2.2 Rainfall impact to Landslides. 8
2.3 Earthquake influences to Landslides. 12
CHAPTER THREE RESEARCH DESIGN AND METHODOLOGY 17
3.1 Landslide Inventory. 18
3.1.1 Data source (image) 19
3.1.2 Semi-auto classification 20
3.1.3 Quality control and validation 22
3.1.4 Variation analysis of landslides 24
3.2 Precipitation record. 26
3.3 Zonal analysis. 30
3.4 Statistical model of new landslide occurrence. 32
3.4.1 Landslide and rainfall 32
3.4.2 Impact of earthquake 33
3.4.3 Antecedent rainfall 34
3.4.4 Model assumption 34
3.4.5 Proposed model 34
3.5 Genetic Algorithm. 35
CHAPTER FOUR RESEARCH RESULTS 40
4.1 Zonal analysis results. 40
4.1.1 Variations in landslide density 40
4.1.2 Variation in the position of landslides on a hill slope 47
4.1.3 Landslide density with respect to the ground motion 49
4.1.4 Summary of zonal analysis 51
4.2 Model Estimation. 52
CHAPTER FIVE CONCLUSION AND SUGGESTIONS 59
CHAPTER SIX REVISION OF THE PROPOSED MODEL 60
6.1 Using of the incremental landslide density 60
6.2 Renewed sample area of precipitation records 61
6.3 Various modifications of model functions 63
6.3.1 Constant-impact model 63
6.3.2 Energy decay form for the earthquake-impact function 64
6.3.3 Decreasing impact factor form of antecedent rainfall 68
6.3.4 Residue model of the impact factor of earthquake 71
6.4 Model applicability 75
6.5 Conclusions of model revision 77
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