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B4-002
10:50
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11:10
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OPTICAL IMAGE CORRELATION AND THE CHARACTERIZATION OF NEAR-FIELD GROUND DEFORMATION IN SURFACE RUPTURING EARTHQUAKES
Precise characterization of the surface slip produced co-seismically in earthquakes, and during the post- and inter-seismic phases of the seismic cycle, is essential for understanding the mechanics of how faults slip. Modern techniques in satellite geodesy, such as GPS and InSAR, provide powerful tools for retrieving surface displacements produced by earthquakes with very high precision. However, GPS measurements are typically very sparse, while InSAR often fails close to faults, where strain gradients are large. Optical Image Correlation is an alternative geodetic technique which allows the retrieval of ground displacements close to earthquake surface ruptures, using sub-pixel correlation of optical satellite (or aerial) images acquired before and after an earthquake. We first review the various developments of this technique up to the present day, before giving examples of how it has been used to study various earthquakes globally (including the 1999 Chi Chi earthquake). Because optical image correlation retrieves the average displacement over a small correlation window of pixels (compared with spot measurements collected in the field), they typically include any off-fault deformation (OFD) which may occur on secondary or distributed structures, as well as the primary deformation localized on the main fault. Comparison of co-seismic displacements measured in the field with those from image correlation for several large strike-slip earthquakes provides a unique opportunity estimate the magnitude of OFD occurring in earthquakes globally. I discuss several case studies (including Landers, Hector Mine, Balouchistan, Norcia, Kaikoura, and Palu earthquakes) where optical image correlation has been used to characterize near-field co-seismic displacements. OFD appears to correlate with total geological offset on strike-slip faults, suggesting an increase in localization and decrease in OFD as faults mature. Better characterization of the magnitude and width over which OFD occurs is essential for the correct assessment of fault slip rates using Quaternary dating techniques, and earthquake slip histories determined with trenching (paleoseismology), which are both key ingredients in seismic hazard assessment. I finish with several examples of future research directions in which optical image correlation can be further developed to provide more detailed and precise 3D measurements of ground deformation over time; with huge potential for studying active fault zones, as well as a wide range of other surface phenomena.
James Hollingsworth
earthquake deformation, fault rupture, optical image correlation, satellite geodesy
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B4-011
11:10
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11:25
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THE 2018 MW6.4 HUALIEN EARTHQUAKE IN EASTERN TAIWAN: INSIGHTS FROM SYNTHETIC APERTURE RADAR INTERFEROMETRY (INSAR) AND RELOCATED SEISMICITY
I attempt at providing new insights about the latest 2018 catastrophic earthquake in Hualien, eastern Taiwan, based on the results from Synthetic Aperture Radar Interferometry (InSAR), relocated seismicity and AutoBATS solution. In this paper, the pre-seismic, co-seismic and post-seismic deformation are investigated using the InSAR processing system based on Generic Mapping Tools, or GMTSAR for short and Sentinel-1 data. Interferometric results suggest that there may exist a geologic structure in and around the Mugua River. By analyzing the relocated seismicity two- and three-dimensionally, a cluster of seismicity with focal depths in between 60 and 80 km is located in and around the upstream of the Mugua River. It is further confirmed that it is the surface manifestation of a minor, near-west-facing subducting slab beneath the region. Both Hualien City and the hypocenter of the 2018 Hualien earthquake lie directly above it. The importance of this paper is that it provides a new insight regarding the tectonic configuration of the study area and the great Wadati-Benioff zone in the northern Taiwan.
Sin-Mei Ng
Hualien earthquake, Radar interferometry, Subducting slab
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B4-013
11:25
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11:40
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DIGITALLY IMAGING SURFACE DEFORMATION: CASE STUDIES OF 1999 CHI-CHI, 2008 WENCHUAN AND 2018 HUALIEN EARTHQUAKES
Earthquakes are the result of releasing accumulation stress on the fault plane underground and large ones often produce surface ruptures and deformations, which are closely related to the fault geometry down beneath. For both the purpose of scientific approach and hazard mitigation, to reconstruct the fault geometry and diagnose related rupture behaviors are topics of great importance nowadays. In order to proceed towards the insights in this research orientation, this study works on the fault geometry and comprehensive process of the fault kinematics in the durations of coseismic. Several different optical images of satellite and aerial photos were applied on real seismic cases. These images are applied by the technique of pixel comparison to generate high resolution mapping of coseismic horizontal displacements. If the vertical displacements can be also generated by other independent methods, the detailed seismogenic fault geometry can be reconstructed by synthesizing above horizontal and vertical component. For the Wenchuan earthquake, the derived amplitude and direction of the surface displacement are of critical assistance to help understand the behavior and propagation of coseismic fault rupturing. For the case of the Chi-Chi earthquake, because the source images are paired aerial photos, the mapping of horizontal displacement can reach a resolution of 100 meters in grid. Also resulted is equivalent high resolution 3D fault geometrical model. The Hualien earthquake is the last case study. Based on the high-resolution Pleiades optical satellite imagery, correlation of pre- and post-earthquake stereo images reveals detailed 3D surface displacements along the 8 km-long Milun Fault. The results suggest the main fault slip (up to 1 m) stopped at very shallow depths below the surface, where ~60% of the deformation may be accommodated as off-fault deformation. As a whole, different images have their own prevailing aspects and weaknesses. The best way to obtain reliable results is to select the most suitable one under the consideration of regional characteristics and various scientific purposes.
Yu-Ting Kuo
earthquake, Fault Geometry, Optical Image, seismogenic structure, Surface Displacement
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A4-012
11:40
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11:55
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ANALYSIS OF PALSAR-2 IMAGES TO EXTRACT GEOLOGICAL EFFECTS CAUSED BY THE 2018 HOKKAIDO-EASTERN-IBURI EARTHQUAKE
An Mw 6.6 earthquake hit the eastern part of Iburi sub-prefecture, Hokkaido, Japan on September 6, 2018. The occurrences of extensive liquefaction were reported in Tomakomai, Sapporo, Kita-Hiroshima cities. In this study, multi-temporal PALSAR-2 images acquired before and after the event were employed to extract ground failures in urban areas. The coherence values were calculated for pre-event and co-event PALSAR-2 image pairs. Comparing with the result of field surveys, the ground failures caused by liquefaction were identified properly by the reduction of coherence.
Fumio Yamazaki, Wen Liu
2018 Hokkaido-Eastern-Iburi earthquake, field survry, liquefaction, PALSAR-2
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