Options
Nercessian, Alexandre
Loading...
Preferred name
Nercessian, Alexandre
3 results
Now showing 1 - 3 of 3
- PublicationRestrictedSeismicity, deformation and seismic hazard in the western rift of Corinth: New insights from the Corinth Rift Laboratory (CRL)(2006)
; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ;This paper presents the main recent results obtained by the seismological and geophysical monitoring arrays in operation in the rift of Corinth, Greece. The Corinth Rift Laboratory (CRL) is set up near the western end of the rift, where instrumental seismicity and strain rate is highest. The seismicity is clustered between 5 and 10 km, defining an active layer, gently dipping north, on which the main normal faults, mostly dipping north, are rooting. It may be interpreted as a detachment zone, possibly related to the Phyllade thrust nappe. Young, active normal faults connecting the Aigion to the Psathopyrgos faults seem to control the spatial distribution of the microseismicity. This seismic activity is interpreted as a seismic creep from GPS measurements, which shows evidence for fast continuous slip on the deepest part on the detachment zone. Offshore, either the shallowest part of the faults is creeping, or the strain is relaxed in the shallow sediments, as inferred from the large NS strain gradient reported by GPS. The predicted subsidence of the central part of the rift is well fitted by the new continuous GPS measurements. The location of shallow earthquakes (between 5 and 3.5 km in depth) recorded on the on-shore Helike and Aigion faults are compatible with 50° and 60° mean dip angles, respectively. The offshore faults also show indirect evidence for high dip angles. This strongly differs from the low dip values reported for active faults more to the east of the rift, suggesting a significant structural or rheological change, possibly related to the hypothetical presence of the Phyllade nappe. Large seismic swarms, lasting weeks to months, seem to activate recent synrift as well as pre-rift faults. Most of the faults of the investigated area are in their latest part of cycle, so that the probability of at least one moderate to large earthquake (M = 6 to 6.7) is very high within a few decades. Furthermore, the region west to Aigion is likely to be in an accelerated state of extension, possibly 2 to 3 times its mean interseismic value. High resolution strain measurement, with a borehole dilatometer and long base hydrostatic tiltmeters, started end of 2002. A transient strain has been recorded by the dilatometer, lasting one hour, coincident with a local magnitude 3.7 earthquake. It is most probably associated with a slow slip event of magnitude around 5 ± 0.5. The pore pressure data from the 1 km deep AIG10 borehole, crossing the Aigion fault at depth, shows a 1 MPa overpressure and a large sensitivity to crustal strain changes.77 1 - PublicationRestrictedAnalysis of eleven years of deformation measured by GPS in the Corinth Rift Laboratory area(2004)
; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ;GPS (Global Positioning System) data collected in the Corinth Rift during eleven campaigns between 1990 and 2001 provide velocities of 57 points with ∼1.5 mmyr−1 accuracy. Peloponnesos moves at 30 mmyr−1 to the N215° E with respect to a fixed Europe. Extension across the rift is accommodated in a narrow band offshore. Its rate increases from east to west and is 16 mmyr−1 near Aigion. Both sides of the rift behave as clockwise rotating blocks with rates of 7±0.5° Myr−1 and 2.8±0.8° Myr−1, respectively for the northern and southern blocks. After removing block rotations, the northern block shows a north–south extension rate of 120±50 nstrainyr−1, whereas the southern block indicates the internal deformation is still inside the error bar (<20 nstrainyr−1). The strain accumulation across the major faults located along the southern coast of the Corinth Gulf is less than 1 mmyr−1. This implies long recurrence periods for large earthquakes on these faults.100 3 - PublicationRestrictedUsing kinematic GNSS data to assess the accuracy and precision of the TanDEM-X DEM resampled at 1 m resolution over the western Corinth Gulf, Greece(2021)
; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ;; We assess the accuracy and the precision of the TanDEM-X digital elevation model (DEM) of the western Gulf of Corinth, Greece. We use for that a dense set of accurate ground coordinates obtained by kinematic GNSS observations. Between 2001 and 2019, 148 surveys were made, at 1 s sampling rate, along highways, roads and tracks, with a total traveled distance of ~25,000 km. The data are processed with the on-line Canadian Spatial Reference System precise point positioning software. From the output files, we select 885,252 coordinates from epochs with theoretical uncertainty below 0.1 m in horizontal and 0.2 m in vertical. Using specific calibration surveys we estimate the mean vertical accuracy of the GNSS coordinates at 0.2 m. Resampling the DEM by a factor of ten allows to compare it with the GNSS in pixels of metric size, thus smaller than the width of the roads, even the small trails. The best fit is obtained by shifting the DEM by 0.47 ± 0.03 m upward, 0.10 ± 0.1 m westward, and 0.36 ± 0.1 m southward. Those values are twenty times below the nominal resolution of the DEM. Once the shift is corrected, the root mean square deviation between TanDEM-X DEM and GNSS elevations is 1.125 m. In forest and urban areas, the shift between the DEM and the GNSS increases by ~0.5 m. The metric accuracy of the TanDEM-X DEM paves the way for new applications for long-term deformation monitoring of this area.168 23