Improved source modelling through combined use of InSAR and GPS under consideration of correlated data errors: application to the June 2000 Kleifarvatn earthquake, Iceland

Simultaneous use of multiple independent data sets can improve constraints on earthquake source-model parameters. However, the ways in which data sets have been combined in the past are manifold and usually qualitative. In this paper we present a method to combine geodetic data in source model estimations, which includes characterizing the data errors and estimating realistic model-parameter uncertainties caused by these errors. We demonstrate this method in a case study of the June 2000 Kleifarvatn earthquake, which occurred on Reykjanes Peninsula in Iceland. We begin by showing to what extent additional data can positively influence the source modelling results, by combining both GPS and descending-orbit InSAR data, which were used in two earlier studies of that event, with InSAR data from an ascending orbit. We estimate the data error covariances of the InSAR observations and base the data weights in our model-parameter optimization on the corresponding data variance-covariance matrix. We also derive multiple sets of synthetic data errors from the estimated data covariances that we use to modify the original data to generate numerous data realizations. From these data realizations we estimate the model-parameter uncertainties. We first model the Kleifarvatn earthquake as a simple uniform-slip fault and subsequently as a fault with variable slip and rake. Our fault model matches well with the field observations of coseismic surface ruptures and its near-vertical dip (83°) agrees with the regional faulting style as well as with aftershock locations. The two published source models of the event, on the other hand, both differ from our model as well as differing for one another. These studies, which were based on the descending InSAR data alone (the first study) and on that same data and GPS data (the second study), both neglect correlations in the InSAR data and do not report model-parameter uncertainties. Therefore, to compare these results with our model, we simulate the earlier model estimation set-ups and provide realistic estimates of the model-parameters uncertainties for these cases. We then discuss the significance of the difference between the existing fault models and demonstrate that both the inclusion of additional independent data as well as the covariance-based data weights improve the model-parameter estimatio

Broadband frequency-dependent amplification of seismic waves across Bucharest, Romania

The determination of seismic amplitude amplification is a fundamental contribution to seismic hazard assessment. While often only high-frequency amplitude variations (>1Hz) are taken into account, we analyse broadband waveforms from 0.14 to 8.6Hz using a temporary network of 32 stations in and around the earthquake-prone city of Bucharest. Spectral amplitudes are calculated with an adaptive multiple-taper approach. Across our network (aperture 25km×25km), we find a systematic northwest/southeast-oriented structural influence on teleseismic P-wave amplitudes from 0.14 to 0.86Hz that can be explained by constructive interference in the dipping Cenozoic sedimentary layers. For higher frequencies (1.4-8.75Hz), more local site effects prevail and can be correlated partly among neighbouring stations. The transition between systematic and localised amplitude variations occurs at about 1H

Source model for the 1997 Zirkuh earthquake (MW: 7.2) in Iran derived from JERS and ERS InSAR observations

We present the first detailed source model of the 1997 M7.2 Zirkuh earthquake that ruptured the entire Abiz fault in East Iran producing a 125 km long, bended and segmented fault trace. Using SAR data from the ERS and JERS-1 satellites we first determined a multisegment fault model for this predominately strike-slip earthquake by estimating fault-segment dip, slip, and rake values using an evolutionary optimization algorithm. We then inverted the InSAR data for variable slip and rake in more detail along the multisegment fault plane. We complement our optimization with importance sampling of the model parameter space to ensure that the derived optimum model has a high likelihood, to detect correlations or trade-offs between model parameters, and to image the model resolution. Our results are in an agreement with field observations showing that this predominantly strike-slip earthquake had a clear change in style of faulting along its rupture. In the north we find that thrust faulting on a westerly dipping fault is accompanied with the strike-slip that changes to thrust faulting on an eastward dipping fault plane in the south. The centre part of the fault is vertical and has almost pure dextral strike-slip. The heterogeneous fault slip distribution shows two regions of low slip near significant fault step-overs of the Abiz fault and therefore these fault complexities appear to reduce the fault slip. Furthermore, shallow fault slip is generally reduced with respect to slip at depth. This shallow slip deficit varies along the Zirkuh fault from a small deficit in the North to a much larger deficit along the central part of the fault, a variation that is possibly related to different interseismic repose time

Interseismic and Postseismic Shallow Creep of the North Qaidam Thrust Faults Detected with a Multitemporal InSAR Analysis

Understanding the mechanisms by which earthquake cycles produce folding and accommodate shortening is essential to quantify the seismic potential of active faults and integrate aseismic slip within our understanding of the physical mechanisms of the long-term deformation. However, measuring such small deformation signals in mountainous areas is challenging with current space-geodesy techniques, due to the low rates of motion relative to the amplitude of the noise. Here we successfully carry out a multitemporal Interferometric Synthetic Aperture Radar analysis over the North Qaidam fold-thrust system in NE Tibet, where eight Mw> 5.2 earthquakes occurred between 2003 and 2009. We report various cases of aseismic slip uplifting the thickened crust at short wavelengths. We provide a rare example of a steep, shallow, 13-km-long and 6-km-wide afterslip signal that coincides spatially with an anticline and that continues into 2011 in response to a Mw 6.3 event in 2003. We suggest that a buried seismic slip during the 2003 earthquake has triggered both plastic an-elastic folding and aseismic slip on the shallow thrusts. We produce a first-order two-dimensional model of the postseismic surface displacements due to the 2003 earthquake and highlight a segmented slip on three fault patches that steepen approaching the surface. This study emphasizes the fundamental role of shallow aseismic slip in the long-term and permanent deformation of thrusts and folds and the potential of Interferometric Synthetic Aperture Radar for detecting and characterizing the spatiotemporal behavior of aseismic slip over large mountainous regions

Permafrost thaw subsidence of Siberian yedoma: field measurements and TerraSAR-X interferometry

In permafrost active layer cycles of excess ice formation in winter and loss in summer result in seasonal vertical movements of the ground in both directions. Additionally, relatively uniform thawing of the ice-rich layer at the permafrost table, contributing to irreversible lowering of the surface, was reported for a number of Arctic locations. We use a simple method to quantify surface lowering (subsidence) and uplift in the Lena River Delta, Siberian Arctic, using more than 30 reference rods (fiberglass and metal) installed deeply in permafrost. We repeatedly measured the length of a rod part, which is emerged above the ground, in 2013-2017. Measurements show seasonal subsidence in a range from 0 to 4.6 cm (median: 1.6 cm; 8 measurements) in the cold summer of 2013 and from 0.8 to 8.6 cm (median: 4.8 cm; 31 measurements) in the warm summer of 2014. A pronounced multi-year subsidence of 9.3±5.7 cm was measured in the end of summer 2017 relative to the initial measurements in spring 2013. Additionally, we observed high spatial variability of subsidence even at the sub-meter scale. Differential Synthetic Aperture Radar Interferometry (DInSAR), most often used to measure ground displacement caused by tectonic or volcanic processes, is adapted now for the detection of subsidence in permafrost. Our study tests the viability of repeat pass (11 days) TerraSAR-X (TSX) data for the detection of thaw subsidence over the same study area. Due to TSX short wavelength and, therefore, shallow penetration depth, interferometry is strongly hampered by poor phase coherence. We built a stack of 11-day interferograms for the summer of 2013 where coherence of some single interferograms was on the edge of the acceptable. The stack showed only a minor subsidence with a mean of 0.3±0.3 cm over the studied area. Given the discrepancy between the DInSAR and field data we discuss the limitations of TSX data for an accurate representation of permafrost thaw subsidence

Improved source modelling through combined use of InSAR and GPS under consideration of correlated data errors: Application to the June 2000 Kleifarvatn earthquake, Iceland

ISSN:0956-540XISSN:1365-246

Source model for the 1997 Zirkuh earthquake (M-W=7.2) in Iran derived from JERS and ERS InSAR observations

ISSN:0956-540XISSN:1365-246