Earth Science and Engineering Ph.D. Dissertation

Abstract

Understanding the geometry, the earthquake history and the rate of deformation of a fault is crucial to assess the seismic behaviour of active faults. In particular, Oceanic Transform Faults (OTFs) lie at the bottom of the oceans making difficult the study of their long-term behaviour. The Húsavík Flatey Fault (HFF) in North Iceland is a partially exposed OTF and therefore is a good laboratory to study the characteristics of an OTF. In this study, we conduct the first paleoseismological and morphotectonic study of the HFF and provide information on the earthquake history and slip rate of the fault. We investigate the occurrence of past earthquakes on the HFF by building the first earthquake catalogue of the HFF for the Holocene period. To do so, we excavated paleoseismological trenches in two locations along the HFF to identify past earthquakes and constrain their timing. Our catalogue suggests a periodic behaviour of the seismicity along the HFF with a return time of a characteristic earthquake of $\sim$ 500 years. Eventually, our catalogue indicates that the characteristic earthquake on the HFF has a maximum magnitude of 7.2 to 7.3. Finally, in order to calculate the slip rate of the fault, we performed detailed morphotectonic analysis at different locations along the HFF, to measure displacement related to fault activity. We measured fault offset of river beds, alluvial fans, glacial moraines and landslides, ranging from 10 cm to 150 m, to constrain the Holocene slip rate of the HFF. Additionally, we measured the offset of the edge of a peninsula to infer the Pleistocene slip rate of the HFF and we estimated the vertical Pleistocene slip rate from the vertical step across a volcanic shield. Combining these displacement measurements with direct dating (radiocarbon and tephra) and ages inferred from literature, we constrain a slip rate of 6 to 6.5 mm/yr on the HFF, steady since at least the late Pleistocene. Our work contributes to the characterization of the seismic behaviour of the HFF by shedding light on the Holocene and late Pleistocene seismic history of the fault, ultimately providing unique insights into the tectonics and earthquake activity of a transform zone.