Abstract
ABSTRACT The Upper Rhine Graben (URG) undergoes continuous microseismicity recorded by seismic monitoring networks and moderate-magnitude earthquakes, such as in the zone north of the Alpine front, which includes the Jura thrust front, the Vosges, the Black Forest, the Swabian Jura and the Alsace plain. The surface velocity field is a good indication of the occurrence and location of strain gradients likely associated with seismogenic structures. To explore that possibility, we use long time-series of displacements measured from 2002 to 2018 with the dense GURN network (GNSS URG Network). The processing based on double differences of phase measurements offers an up-to-date surface velocity field of the URG and surrounding areas. The surface velocity field relative to the Eurasia reference frame (ITR2014) points out some areas where coherent movements are present for groups of stations. The heterogeneous velocity field across the Rhine Graben (Vosges, URG, Black Forest and Swabian Jura) displays velocity values below 0.2 mm yr−1. We compute a deformation field from the GNSS velocities to link the deformation to the spatial distribution of earthquakes in the Rhine Graben. The earthquakes are concentrated south of an east–west line passing through Strasbourg to the Alpine front. Instrumental and historical seismicity presents spatial similarities in the Vosges and Swabian Jura. Considering the consistent northward movement observed in the Alpine front, we suggest that the strong seismicity in the south of the URG is caused by the shortening of the Alps. North of the URG, the seismicity is more dispersed where the velocity field does not show coherent movements.
Highlights
Recent compilations of data acquired by numerous GNSS stations clearly show a strong contrast between the southern and northern regions of Western Europe
We focus on the geodetic signal observed within the Upper Rhine Graben (URG) and surrounding regions, considering its potential relationships to seismic activity
The lack of current geodetic deformation observed across the URG area along an SW-NE axis and from the region extending from Strasbourg to Karlsruhe in particular, suggests that both historical and instrumental events cannot be explained by significant measurable current tectonic movements observed from geodetic data
Summary
We establish an updated surface velocity field for the URG by processing GNSS data from a dense permanent network over the 2002–2018 period. From GNSS and levelling data, Furhmann et al (2013) conducted a regional analysis of the URG. Furhmann et al (2015) focused on the northern part of the URG by combining GNSS, levelling and InSAR data. By computing more recent GNSS data we aim to precisely quantify the surface deformation affecting this region, where horizontal and vertical surface velocities are small and of the same order as their uncertainties. The spatial density determined by the sites of the GNSS Upper Rhine Network (GURN) allows the analysis of geodetic signals over a large area, and the longer period of data recording offers the opportunity to obtain more reliable results
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