Interseismic deformation of the Húsavík–Flatey fault (North Iceland) from two decades of GNSS data

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SUMMARY The Tjörnes Fracture Zone in North Iceland is one of two transform zones in Iceland capable of generating earthquakes of magnitude $\sim$7. More than 150 years have passed since the last two major earthquakes occurred on the Húsavík–Flatey fault, one of the two main transform structures within the Tjörnes Fracture Zone. Given the seismic hazard posed to Húsavík and adjacent coastal communities, accurately determining the slip rate and locking depth of this fault is crucial for a robust earthquake hazard and risk assessment. In this study, we significantly expand the existing global navigation satellite system data set for the Tjörnes Fracture Zone by incorporating more than a decade of additional data and doubling the number of stations. This expansion not only improves the spatial coverage of the network, but also refines the station velocities. We present an updated interseismic velocity field for North Iceland and implement a backslip model with nine dislocation segments to describe the plate boundary deformation. Additionally, we include a point pressure source for the ongoing broad uplift signal in the study area. Our findings indicate a locking depth of $7.3\substack{+0.9 \\ -0.7}$ km and an average slip rate of $6.9\pm 0.2$ mm yr−1 for the Húsavík–Flatey fault. With our updated approach, we can narrow down model parameter constraints from previous studies and thereby provide an enhanced understanding of the earthquake potential of this region.

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