Chapter 1 General Introduction and Methodology 1
1.1 Purposes of this work 1
1.2 Seismic tomography 5
1.2.1 Model parameterization 6
1.2.2 Fast ray tracing 8
1.2.3 Tomographic inversion 11
1.2.4 Damped least squares method 13
1.2.5 Error and resolution analyses 15
1.3 Hypocenter location 16
1.3.1 sP-depth phase 19
1.3.2 Double-difference location method 19
1.3.3 Master-event location method 24
1.4 Tectonic setting of the western Pacific island arcs 31
Chapter 2 Velocity Structures under the Entire-arc Regions of Northern Japan and Hokkaido 33
2.1 Introduction 33
2.2 Previous studies 34
2.3 Data and method 35
2.3.1 Data 35
2.3.2 Method 36
2.3.3 Ray tracing for the sP-depth phase 38
2.4 Resolution and results 38
2.5 Discussion 41
2.5.1 Hypocentral locations of the suboceanic earthquakes 41
2.5.2 Velocity structures in the crust and mantle wedge 46
2.5.3 Structural heterogeneity in the forearc region 52
2.5.4 Interplate earthquakes on the slab boundary 53
2.5.5 Serpentinization of the forearc mantle 54
2.6 Summary 54
Chapter 3 Offshore Earthquake Location:Methodology and Application 56
3.1 Introduction 56
3.2 Tectonic background of the study region 57
3.3 Methods 58
3.3.1 Hypocenter location of the master events 58
3.3.2 Extension of the double-difference technique 59
3.4 Offshore earthquake location off the central Japan 61
3.5 Tomographic inversion 64
3.6 Discussion 67
3.6.1 Interpretations of the tomographic images 67
3.6.2 Volcanoes,large earthquakes,and the subducting slabs 72
3.7 Summary 76
Chapter 4 Role of Fluids on the Low Frequency Tremors in Southwest Japan 77
4.1 Introduction 77
4.2 Tectonic setting of the Nankai subduction zone 78
4.3 Data and method 79
4.4 Resolution and results 82
4.5 Interpretation and discussion 86
4.5.1 Structure heterogeneities along the LFT belt 86
4.5.2 Generating mechanism of the low frequency tremors 91
4.6 Summary 94
Chapter 5 New Insight into Arc Volcanism and Forearc Seismotectonics in Kyushu 96
5.1 Introduction 96
5.2 Data and method 98
5.3 1-D velocity model 99
5.4 Synthetic tests for locating the offshore earthquakes 100
5.5 Resolution and results 103
5.6 Discussion 106
8.7 Summary 170
Chapter 9 New Insight into Structural Heterogeneity beneath Taiwan 171
9.1 Introduction 171
9.2 Tectonic setting 173
9.3 Dataand methods 173
9.4 Relative residuals of the teleseismic data 178
9.5 1-D velocity model and resolution tests 179
9.6 Discussions 185
9.6.1 Structural heterogeneity,seismicity and plate coupling 185
9.6.2 Direct evidence for the subducted Eurasian lithosphere 194
9.7 Summary 199
Chapter 10 Concluding Remarks 203
References 206