Investigating the earthquake cycle of normal faults

Geodetic observations of crustal deformation through the earthquake cycle provide unique opportunities to gain essential knowledge of faulting mechanisms, lithospheric rheology, and fault interaction. Normal faults, an integral geologic unit responsible for crustal deformation, are specifically investigated in this thesis, via three case studies in two significantly different tectonic environments: the 2008 Mw 6.3 Damxung and Mw 7.1 Yutian earthquakes on the Tibetan Plateau, and the 2005 Mw 7.8 Tarapaca earthquake in the northern Chile subduction zone. To move toward realistic slip models, I consider crustal layering for the Damxung earthquake, and non-planar rupture for the Yutian earthquake. The Damxung study shows that assuming a homogeneous crust underestimates the depth of slip and overestimates the magnitude, in comparison to a crustal model with a weak sedimentary lid. A curved fault model composed of triangular dislocation elements (TDEs) for the Yutian earthquake recovers the geodetic observation better than rectangular fault segments. Normal faulting earthquakes are characterized by shallow slip deficit, which is partially compensated by patchy afterslip around, but no deeper than, the coseismic rupture. The complementary and partially-overlapping relationship between coseismic slip and afterslip implies complexity of frictional properties in both down-dip and along-strike directions. Postseismic deformation induced by viscoelastic relaxation (VER) following normal faulting earthquakes is fundamentally different in pattern from that produced by afterslip. This difference enables identification of afterslip as the major postseismic mechanism for the Damxung and Yutian earthquakes, and VER for the Tarapaca earthquake. In addition to understanding the faulting mechanism, I also place constraints on local rheological structure. In central Tibet, where the Damxung earthquake occurred, lack of noticeable VER-related signal allows a lower bound of 1 × 1018 Pa s for the viscosity of the lower crust/upper mantle. In northern Chile, geodetic observations following the Tarapaca earthquake indicate a weak layer with viscosity of 4 – 8 × 10^18 Pa s beneath a higher-viscosity lower crust and mantle lithosphere, and a strong continental forearc. Based on the co- and post-seismic models, I investigate fault interaction from a perspective of static stress change. Stress computation suggests that the 2014 Mw 6.9 strike-slip event close to the Altyn Tagh fault occurred on a fault that was positively stressed by the Yutian earthquake, and the Altyn Tagh fault to the east of the 2014 rupture is a potential locus for future failure. Although the Coulomb stress change on the 2014 Iquique earthquake rupture is negative due to the Tarapaca earthquake and its postseismic VER process, positive loading on the shallow-dipping nodal plane of its M 6.7 preshock suggests that the Tarapaca earthquake may have acted as an indirect trigger of the 2014 Iquique earthquake. Both studies reveal the role played by normal faults in interacting with other types of faults and have implications for seismic hazard assessment

Investigating the postseismic deformation of strike-slip earthquakes on the Tibetan Plateau

InSAR is a useful technique to detect large-scale surface deformation from space. To place constraints on the rheological structure of the lithosphere in the Tibetan Plateau, two strike-slip earthquakes have been investigated. One is the Mw 7.6 Manyi earthquake, which occurred in the north-central Tibetan Plateau. The other is the Mw 6.5 Jiuzhaigou earthquake, which happened that on the eastern part of the Tibetan Plateau. My InSAR data cover 12 years following the Manyi earthquake, much longer than previous researchers’ dataset. I test three viscoelastic models (Maxwell, Standard linear solids, and Burgers body) and one afterslip model. The viscoelastic models cannot match the observed temporal–spatial deformation patterns. The distributions of deformation in the viscoelastic models extend into the far field and the residuals tend to increase, which are inconsistent with the data. The afterslip model has the lowest misfit and explains the temporal and spatial pattern of the observed deformation with decent result. A combined model that considers the effects of both afterslip and viscoelastic relaxation has also been tested. In this combined model, the viscoelastic relaxation that occurs with an elastic layer of thickness of 30 km over a half-space place, produce an estimate for viscosity of 5 × 1019 Pa s for this area. Therefore, either the afterslip model or the combined model can be used to explain the 12 years postseismic deformation of Manyi earthquake. The long time series of the Manyi earthquake enable us to distinguish between afterslip and viscoelastic relaxation. The seismogenic fault of the Jiuzhaigou earthquake was previously unidentified and no surface rupture is found after the earthquake. I first determined the fault geometry and calculated coseismic slip model. The slip model indicates a left-lateral strike-slip pattern, which is consistent with focal mechanisms were determined by different agencies. There is no visible postseismic deformation signal of the fault, which means the surface deformation generated by fault creeping is smaller than the noise of our observation method over that period. Therefore, I try to find the lower bound of the viscosity for this area. My preferred minimum possible viscosity of the underlying half-space is ∼6 × 1017 Pa s. Together with previous geodetic studies, the viscosities obtained from central Tibet show at least one order of magnitude difference with the viscosities obtained from the eastern Tibet. The heterogeneity indicates the rheology has a relatively large spatial change through the whole Plateau. The viscoelastic model always been proposed to explain long-term postseismic deformation and afterslip is used to explain the short-term deformation or localised deformation. Sometimes, the viscoelastic deformation signal is invisible in the moderate earthquakes as the stress is not large enough to generate observable deformation

Modelling co- and post-seismic displacements revealed by InSAR, and their implications for fault behaviour

The ultimate goal of seismology is to estimate the timing, magnitude and potential spatial extent of future seismic events along pre-existing faults. Based on the rate-state friction law, several theoretical physical earthquake models have been proposed towards this goal. Tectonic loading rate and frictional properties of faults are required in these models. Modern geodetic observations, e.g. GPS and InSAR, have provided unprecedented near-field observations following large earthquakes. In theory, according to the frictional rate and state asperity earthquake model, velocity-weakening regions holding seismic motions on faults should be separated with velocity-strengthening regions within which faults slip only aseismically. However, early afterslip following the 2011 MW 9.1 Tohoku-Oki earthquake revealed from GPS measurements was largely overlaid on the historical rupture zones, which challenged the velocity weakening asperity model. Therefore, the performance of the laboratory based friction law in the natural events needs further investigation, and the factors that may affect the estimates of slip models through geodetic modelling should also be discussed systematically. In this thesis, several moderate-strong events were investigated in order to address this important issue. The best-fit co- and post-seismic slip models following the 2009 MW 6.3 Haixi, Qinghai thrust-slip earthquake determined by InSAR deformation time-series suggest that the maximum afterslip is concentrated in the same area as the coseismic slip model, which is similar to the patterns observed in the 2011 Japan earthquake. In this case, complex geometric asperity may play a vital role in the coseismic nucleation and postseismic faulting. The major early afterslip after the 2011 MW 7.1 Van mainshock, which was revealed by one COSMO-SkyMed postseismic interferogram, is found just above the coseismic slip pattern. In this event, a postseismic modelling that did not allow slip across the coseismic asperity was also tested, suggesting that the slip model without slip in the asperities can explain the postseismic observations as well as the afterslip model without constraints on slip in the asperities. In the 2011 MW 9.1 Tohoku-Oki earthquake, a joint inversion with the GRACE coseismic gravity changes and inland coseismic GPS observations was conducted to re-investigate the coseismic slip model of the mainshock. A comparison of slip models from these different datasets suggests that significant variations of slip models can be observed, particularly the locations of the maximum slips. The joint slip model shows that the maximum slip of ~42 m appears near the seafloor surface close to the Japan Trench. Meanwhile, the accumulative afterslip patterns (slip >2 m) determined in previous studies appear in spatial correlation with the Coulomb stress changes generated using the joint slip model. As a strike-slip faulting event, the 2011 MW 6.8 Yushu earthquake was also investigated through co- and post-seismic modelling with more SAR data than was used in previous study. Best slip models suggest that the major afterslip is concentrated in shallow parts of the faults and between the two major coseismic slip patterns, suggesting that the performance of the rate and state frictional asperity model is appropriate in this event. Other postseismic physical mechanisms, pore-elastic rebound and viscoelastic relaxation have also been examined, which cannot significantly affect the estimate of the shallow afterslip model in this study. It is believed that the shallow afterslip predominantly controlled the postseismic behaviour after the mainshock in this case. In comparison to another 21 earthquakes investigated using geodetic data from other studies, complementary spatial extents between co- and post-seismic slip models can be identified. The 2009 MW 6.3 Qinghai earthquake is an exceptional case, in which the faulting behaviours might be dominated by the fault structure (e.g. fault bending). In conclusion, the major contributions from this thesis include: 1) the friction law gives a first order fit in most of natural events examined in this thesis; 2) geometric asperities may play an important role in faulting during earthquake cycles; 3) significant uncertainties in co- and post-seismic slip models can appreciably bias the estimation of fault frictional properties; 4) new insights derived from each earthquake regarding their fault structures and complex faulting behaviours have been observed in this thesis; and (5) a novel package for geodetic earthquake modelling has been developed, which can handle multiple datasets including InSAR, GPS and land/space based gravity changes

Application of Small Baseline Subset (SBAS)-INSAR Technique to Study Surface Deformation Due to The Grindulu Fault Activities using Sentinel-1 Data

Numerous variables contribute to the deformation; for instance, local thrust movements, human-made activities, and seismic activity along the Grindulu Fault. The Meteorological, Climatological, and Geophysical Agency of Indonesia (BMKG) reported seismic activities in Pacitan were delivered following November 7, 2019, earthquake, which could indicate the existence of the Grindulu Fault. The location of Grindulu Fault is in the Pacitan Regency on the Southern Coast of Java which directly faces the South Java Subduction zone. In this research, we identify fault activities through the detection around the Grindulu Fault to reduce the disaster risk in Pacitan Regency. Twenty-three ascending Sentinel-1B images and Small Baseline Subset InSAR technique were used to monitor ground deformation in Pacitan Regency between 2019 and 2021. SBAS-InSAR is one of the approaches for analysis techniques that can provide techniques continuous measurements of the ground deformation; it produces mean LOS velocity throughout the Line of Sight (LOS) around the Grindulu Fault segment. The processing was carried out using the GMTSAR software and compared the result using SBAS generated by open-source LiCSBAS of open-source SAR processing result showed deformation in the form of land subsidence in almost all of the Pacitan, with the mean velocity ranging from –2.1 to -43.1 mm/yr. The cause of deformation is the same thing, the existing Grindulu fault. The SBAS result confirmed with geological and geomorphological conditions such Triangular facets, braided rivers, and depression zone near Grindulu fault. Furthermore, the comparison results with the mean LOS velocity from LiCSBAS show that the area around Grindulu Fault also experiences land subsidence. Even though the RMSE value obtained is 13.7 mm/yr, it is demonstrating that the SBASInSAR velocity generated by GMTSAR processing not enough corresponds to the LiCSBAS. ======================================================================================================================================== Banyak variabel berkontribusi pada deformasi; misalnya, gerakan tektonik lokal, atau bahkan aktivitas manusia maupun seismik di sepanjang Sesar Grindulu. Badan Meteorologi, Klimatologi, dan Geofisika Indonesia (BMKG) melaporkan aktivitas seismik di Pacitan terdeteksi yakni berupa gempabumi pada 7 November 2019, yang dapat menjadi indikasi keberadaan Sesar Grindulu. Letak Sesar Grindulu berada di Kabupaten Pacitan dekat dengan Pesisir Selatan Jawa dan berhadapan langsung dengan zona Subduksi Selatan Jawa. Pada penelitian dilakukan identifikasi aktivitas sesar melalui deformasi yang terjadi di sekitar Sesar Grindulu, sehingga dapat mengurangi risiko bencana di Kabupaten Pacitan. Dua puluh tiga citra ascending Sentinel-1B dan teknik Small Baseline Subset InSAR digunakan untuk memantau deformasi tanah di Kabupaten Pacitan antara tahun 2019 dan 2021. SBAS-InSAR adalah salah satu pendekatan untuk memberikan pengukuran deformasi tanah secara kontinu dalam bentuk rata-rata kecepatan deformasi disepanjang Line of Sight (LOS). Pemrosesan dilakukan dengan menggunakan perangkat lunak GMTSAR yang kemudian dibandingkan dengan menggunakan SBAS yang dihasilkan oleh perangkat lunak open source, LiCSBAS. Hasil pengolahan GMTSAR menunjukkan deformasi berupa penurunan muka tanah di hampir seluruh wilayah Pacitan, dengan kecepatan rata-rata berkisar antara –2,1 hingga -43,1 mm/tahun. Penyebab deformasi adalah hal yang sama, yaitu keberadaan sesar Grindulu. Hasil SBAS terkonfirmasi dengan kondisi geologi dan geomorfologi berupa triangular facets, bentuk aliran sungai, dan zona depresi di dekat sesar Grindulu. Selain itu, hasil perbandingan nilai rata-rata kecepatan LOS LiCSBAS menunjukkan bahwa di sekitar Sesar Grindulu juga mengalami penurunan muka tanah. Meskipun nilai RMSE yang diperoleh adalah 13,7 mm/tahun, hal ini menunjukkan bahwa nilai SBASInSAR yang dihasilkan oleh pengolahan GMTSAR belum cukup sesuai dengan hasil LiCSBAS

Geomorphic Evolution of the Nushki Segment of the Chaman Fault in Western Pakistan

The Chaman strike-slip fault marks the western boundary of the collision zone between the Indian and Eurasian plates. It accommodates both lateral translation and convergence of the Indian plate beneath the Eurasian plate and connects the Makran subduction zone to the Himalayan convergence zone. The geomorphic evolution of this very important tectonic feature is relatively unknown compared to other tectonically important faults in the Himalayas such as the Altyn-Tagh and Karakoram faults. The Nushki Basin marks the southern portion of the of the Chaman fault where strike-slip and thrust faults interaction predominates. This work utilizes a morphometric approach towards understanding the geomorphic evolution of the southern segment of the Chaman fault. Fifteen meter Digital Elevation Models (DEM), Advanced Spaceborne Thermal Emission and Reflection (ASTER), and GeoEye-1 satellite images were all integrated to measure three geomorphic indices; stream-length gradient index (SL), mountain-front sinuosity (Smf), and valley-floor width to height ratio (Vf). Analysis of results obtained from the measured indices shows that evolution of landforms in the area is tectonically controlled with propagation of thrust towards the northern flanks of the basin. This is further supported by the results of topographic analysis carried out on a ridge which shows two wind gaps in the north and a corresponding water gap further south. Measured offsets on Quaternary landforms also vary from the northern to southern flanks of the basin, generally showing a larger total displacement in the northern portion relative to the south.Earth and Atmospheric Sciences, Department o

Investigation of lithospheric structure in Mongolia fault: InSAR observations and modelling

Western Mongolia is a seismically active intracontinental region, with ongoing tectonic activity and widespread volcanism attributed to the India-Eurasia collision. During the last century, four M > 8 earthquakes have occurred in Mongolia, which provides opportunities to study how continents deform. The 1957 Gobi-Altai earthquake is one of the largest magnitude earthquakes. The rupture pattern associated with this earthquake is complex, involving left-lateral strike-slip and reverse dip-slip faulting on several distinct geological structures in a 264 × 40 km wide zone. To understand the relationship between observed postseismic surface deformation and the rheological structure of the upper lithosphere, Interferometric Synthetic Aperture Radar (InSAR) data was used to study the 1957 earthquake in southwest of Mongolia and model the late postseismic deformation. SAR data were acquired from the ERS1/2 and Envisat from 1996 to 2010. Using the Repeat Orbit Interferometry Package (ROI_PAC), 124 postseismic interferograms have been produced on four adjacent tracks. Stacking these interferograms yields a maximum InSAR line-of-sight deformation rate along the fault o

Active tectonics and palaeoseismicity of the Northern Tien Shan and Dzhungaria

This thesis focuses on the active tectonics and the palaeoseismicity around the Dzhungarian Basin. The study of surface ruptures is crucial to comprehending the earthquake occurrences of faults. I investigate geomorphic displacements along the boundary strike-slip Dzhungarian Fault using high-resolution drone and Pléiades satellite imagery. The results reveal possible single-event fault slip along the Dzhungarian Fault in the most recent earthquake. I suggest this earthquake is likely linked with a previously identified palaeo-earthquake rupture on the Lepsy Fault. With a joint rupture of the two faults, it could generate an earthquake with a magnitude up to Mw 8.4, which would be amongst the largest magnitude inferred for a continental earthquake. I further use Quaternary dating techniques and InSAR time-series analysis to determine the geological and geodetic slip rates of the Dzhungarian Fault. The results show that the northern Dzhungarian Fault has a long-term uplift rate of 0.6 ± 0.2 mm/yr, whilst the southern Dzhungarian Fault has geological and geodetic strike-slip rates consistent with a range of 2.1 – 4.7 mm/yr. I also re-investigate three historical earthquakes with magnitudes greater than Mw 7.0: the 1812 Nilke, the 1906 Manas and the 1944 Xinyuan Earthquakes in the Borohoro Shan. By re-analysing source parameters and integrating published data, seismological analysis results, and remote-sensing mapping, the study demonstrates the significance of both reverse and strike-slip faulting in the regional seismotectonics, which also indicates the deformation kinematics of the Borohoro Shan as being in a transpressional zone. I collate my results with those from the literature to propose updated earthquake scaling relationships of intra-continental earthquakes. Finally, this study suggests that the Dzhungarian Basin and its surrounding tectonic units are rotating anticlockwise to accommodate both the N-S crustal shortening and the left-lateral shearing within a large-scale zone from the SW Tien Shan to the Altay Mountains

Generic interferometric synthetic aperture radar atmospheric correction model and its application to co- and post-seismic motions

PhD ThesisThe tremendous development of Interferometric Synthetic Aperture Radar (InSAR) missions in recent years facilitates the study of smaller amplitude ground deformation over greater spatial scales using longer time series. However, this poses more challenges for correcting atmospheric effects due to the spatial-temporal variability of atmospheric delays. Previous attempts have used observations from Global Positioning System (GPS) and Numerical Weather Models (NWMs) to separate the atmospheric delays, but they are limited by (i) the availability (and distribution) of GPS stations; (ii) the time difference between NWM and radar observations; and (iii) the difficulties in quantifying their performance. To overcome the abovementioned limitations, we have developed the Iterative Tropospheric Decomposition (ITD) model to reduce the coupling effects of the troposphere turbulence and stratification and hence achieve similar performances over flat and mountainous terrains. Highresolution European Centre for Medium-Range Weather Forecasts (ECMWF) and GPS-derived tropospheric delays were properly integrated by investigating the GPS network geometry and topography variations. These led to a generic atmospheric correction model with a range of notable features: (i) global coverage, (ii) all-weather, all-time usability, (iii) available with a maximum of two-day latency, and (iv) indicators available to assess the model’s performance and feasibility. The generic atmospheric correction model enables the investigation of the small magnitude coseismic deformation of the 2017 Mw-6.4 Nyingchi earthquake from InSAR observations in spite of substantial atmospheric contamination. It can also minimize the temporal correlations of InSAR atmospheric delays so that reliable velocity maps over large spatial extents can be achieved. Its application to the post-seismic motion following the 2016 Kaikoura earthquake shows a success to recover the time-dependent afterslip distribution, which in turn evidences the deep inactive subduction slip mechanism. This procedure can be used to map surface deformation in other scenarios including volcanic eruptions, tectonic rifting, cracking, and city subsidence.This work was supported by a Chinese Scholarship Council studentship. Part of this work was also supported by the UK NERC through the Centre for the Observation and Modelling of Earthquakes, Volcanoes and Tectonics (COMET)

Measuring and modelling the earthquake deformation cycle at continental dip-slip faults

In order for an earthquake to become a natural disaster, it needs to be significantly large, close to vulnerable populations or both. The largest earthquakes in the world occur in subduction zones, where cool, shallowly dipping fault planes enable brittle failure over a large area. However, these earthquakes often occur far away from major cities, reducing their impact. Similar, low angle fault planes can be found in continental fold and thrust belts, where sub-horizontal decollements offer large potential rupture areas. These seismic sources are often much closer to major urban centres than off-shore subduction zone sources. It is therefore essential to understand the processes that control how strain is accommodated and released in such settings. Much of our current understanding of the earthquake cycle comes from studying strike-slip faults. Can our knowledge of strike-slip faults be transferred over to dip-slip faults, and in particular, fold and thrust belts? Previous work has suggested that there may be significant differences between strike-slip and dip-slip settings, and therefore further study of the earthquake cycle in dip-slip environments is required. The recent launch of Sentinel-1, and the extensive Synthetic Aperture Radar (SAR) archive of the European Space Agency (ESA), offer an opportunity to obtain measurements of strain in dip-slip environments that can contribute to our understanding. In this thesis, I use geodetic measurements to contribute to our understanding of the earthquake cycle. Enhanced surface deformation rates following earthquakes (so called postseismic deformation) show temporal and spatial variation. Such variation can be used to investigate the material properties of faults and the surrounding medium. I collate measurements of postseismic velocity following contintental earthquakes to examine the temporal evolution of strain following an earthquake over multiple timescales. The compilation show a simple relationship, with velocity inversely proportional to time since the earthquake. This relationship holds for all fault types, with no significant difference between dip-slip and strike-slip environments. Such lack of difference implies that, at least in terms of the temporal evolution of near field postseismic deformation, both environments behave similarly. I compare these measurements with the predictions of various models that are routinely used to explain postseismic deformation. I find that the results are best explained using either rate-strengthening afterslip or power-law creep in a shear zone with high stress exponent. Such a relationship indicates that fault zone processes dominate the near-field surface deformation field from hours after an earthquake to decades later. This implies that using such measurements to determine the strength of the bulk lithosphere should only be done with caution. I then collate geodetic measurements from throughout the earthquake cycle in the Nepal Himalaya to constrain the geometry and frictional properties of the fault system. I use InSAR to measure postseismic deformation following the 2015 Mw~7.8 Gorkha earthquake and combine this with Global Navigation Satellite System (GNSS) displacements to infer the predominance of down-dip afterslip. I then combine these measurements with coseismic and interseismic geodetic data to determine fault geometries which are capable of simultaneously explaining all three data sets. Unfortunately, the geodetic data alone cannot determine the most appropriate geometry. It is therefore necessary to combine such measurements with other relevant data, along with the expertise to understand the uncertainties in each data set. Such combined measurements ought to be understood using physically consistent models. I developed a mechanically coupled coseismic-postseismic inversion, based on rate and state friction. The model simultaneously inverts the coseismic and postseismic surface deformation field to determine the range of frictional properties and coseismic slip which can explain the data within uncertainties. I applied this model to the geodetic data compilation in Nepal and obtained a range of values for the rate-and-state 'a' parameter between 0.8 - 1.6 x 10^-3, depending on the geometry used. Whilst the Nepal Himalaya is well instrumented, many continental collision zones suffer from a severe lack of data. The Sulaiman fold and thrust belt is one such region, with very sparse GNSS data, but significant seismicity. I apply InSAR to part of the Sulaiman fold and thrust belt near Sibi to examine the evolution of strain throughout the seismic cycle. I tie together observations from ERS, Envisat and Sentinel-1 to produce a time series of displacements over 25 years long which covers an earthquake which occurred in 1997. Using this time series, I investigate the contributions of different parts of the earthquake cycle to the development of topography. I find that postseismic deformation plays a clear role in the construction of short wavelength folds, and that the combination of coseismic and postseismic deformation can reproduce the topography over a variety of lengthscales. The shape of the frontal section of the fold and thrust belt, including the gradient of the topography, is roughly reproduced in a single earthquake cycle. This suggests that fold and thrust belts can maintain their taper in a single earthquake cycle, rather than through earthquakes occurring at different points throughout the belt. I find that approximately 1000 earthquakes like the 1997 event, along with associated postseismic deformation, can reproduce the topography seen today to first order. Such a result may aid our use of topography as a long-term record of earthquake cycle deformation. I finish by drawing these various findings together and commenting on common themes. Afterslip plays an important role in the earthquake cycle, contributing to the surface deformation field in multiple locations, over multiple timescales, and generating topography. This afterslip can be explained using a rate-strengthening friction law with a*sigma between 0.2 and 1.54 MPa. Combining this rate dependence with the static coefficient of friction determined from other methods, such as critical taper analysis, would enable a more complete picture of fault friction to be determined. Fault geometry in fold and thrust belts may control the size of potential ruptures, with junctions and changes in dip angle potentially arresting ruptures. In order to fully determine the role of fault geometry and friction in controlling the earthquake cycle in dip-slip settings, I suggest a more thorough exploitation of the wealth of InSAR data which is now available. These data then need to be combined with measurements from other fields, and models produced which are consistent within the uncertainties of each data set. I suggest that measurements of topography and insights from structural geology may help with understanding the long term and short term processes governing earthquake patterns in an area. As both observations and models are developed, interdisciplinary teams may be able to better constrain the key controls on earthquake hazard in continental dip-slip settings

An investigation of ongoing displacements of active faults in the Gobi desert using persistent scatterer interferometric synthetic aperture radar technique to support the permanent disposal of high-level waste in Beishan, China

This research demonstrated the application of PSInSAR method in identifying and characterising the micro-displacements along active faults in Beishan to support the selection of GDF host rock. This research first distinguishes and separates the tectonic induced and non-tectonic induced deformation within three study areas at Suanjingzi, Jiujing and Xinchang. Through the application of coherence change detection, it found the granite outcrop areas characterised by high coherence provide more robust results of tectonic activity. The Quaternary sediments covered areas which are characterised by low coherence usually show higher deformation rates due to the impacts of erosion and deposition. The tectonic induced displacements generally range from -0.4 to 0.4 mma-1 and are dominated by fault bound tectonic movements. As a part of wrench faut zone, Beishan is impacted by a NE-SW trended maximum in situ compressive stress field (σ1). To correlate the visible valleys, gullies, or cracks in Google Earth imagery with the SAR image deformation discontinuities, this study mapped and characterised more than 40 active faults in the three study areas, these include (1) the NE-SW trended sinistral strike-slip faults triggered by extension and (2) the NW-SE/W-E trended reverse faults triggered by maximum compression. The fault activity is characterised by subtle (minor) displacement rate value difference between the two sides of the fault plane. This research successfully improved the understanding of local structural geology and provided moderate guidance for the selection of HLW disposal sites in China. It was indicated that Xinchang has the highest tectonic stability, and this is then followed by Jiujing and Suanjingzi. This kind of displacement rate difference is possible due to the angle difference towards the Sanweishan Fault Zone. To trace and characterise the undiscovered active fault planes, the PSInSAR approach also benefits the prediction of earthquake by improving the positioning of the potential epicentres.Open Acces