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Université de Neuchâtel

A Long-Lasting Relaxation of Seismicity at Aswan Reservoir, Egypt, 1982-2001

Mekkawi, Mahmoud ; Grasso, J.-R. ; Schnegg, Pierre-André

In: Bulletin of the Seismological Society of America, 2004, vol. 94, no. 2, p. 479-492

The Aswan reservoir seismicity is accepted as an example of reservoir-induced seismicity with the M 5.4 event of 1981, which occurred 15 years after the reservoir impoundment started. During the 1982-2001 period, the Aswan seismicity separates into shallow and deep seismic zones, between 0 and 15 and 15 and 30 km, respectively. These two seismic zones behave differently over time, as...

Université de Neuchâtel

Microscopic scale conductivity as explanation of magnetotelluric results from the Alps of Western Switzerland

Losito, Gabriella ; Schnegg, Pierre-André ; Lambelet, Candice ; Viti, Cecilia ; Trova, Antonello

In: Geophysical Journal International, 2001, vol. 147, no. 3, p. 602–609

Recent MT soundings carried out in the Penninic Alps of Valais have shown the presence of a very good, outcropping conductor. Extremely high conductivity was attributed to the presence of graphite. To verify this assumption, the electrical properties of borehole black shales were measured under simulated physical conditions (electrical frequency, hydrostatic confining pressure, internal...

Université de Neuchâtel

Conductive structures around Las Cañadas caldera, Tenerife (Canary Islands, Spain): A structural control

Coppo, Nicolas ; Schnegg, Pierre-André ; Falco, Pierik ; Costa, Roberto

In: Geologica Acta, 2010, vol. 8, no. 1, p. 67-82

External eastern areas of the Las Cañadas caldera (LCC) of Tenerife (Canary Islands, Spain) have been investigated using the audiomagnetotelluric (AMT) method with the aim to characterize the physical rock properties at shallow depth and the thickness of a first resistive layer. Using the results of 50 AMT tensors carried out in the period range of 0.001 s to 0.3 s, this study provides six...

Université de Neuchâtel

Structural pattern of the western Las Cañadas caldera (Tenerife, Canary Islands) revealed by audiomagnetotellurics

Coppo, Nicolas ; Schnegg, Pierre-André ; Falco, Pierik ; Costa, Roberto ; Burkhard, Martin

In: Swiss Journal of Geosciences, 2008, vol. 101, no. 2, p. 409-413

The local and regional structural pattern of volcanic edifices strongly controls the space distribution of electrical resistivity. Here we report on the structural context of the western part of the Las Cañadas caldera of Tenerife (LCC) thought to have initiated the formation of the caldera. Using a new dataset of 11 audiomagnetotelluric tensors we emphasize the resistivity distribution of...

Université de Neuchâtel

Multiple caldera collapses inferred from the shallow electrical resistivity signature of the Las Cañadas caldera, Tenerife, Canary Islands

Coppo, Nicolas ; Schnegg, Pierre-André ; Heise, Wiebke ; Falco, Pierik ; Costa, Roberto

In: Journal of Volcanology and Geothermal Research, 2008, vol. 170, no. 3-4, p. 153-166

The Las Cañadas caldera of Tenerife (LCC) is a well exposed caldera depression filled with pyroclastic deposits and lava flows from the active Teide–Pico Viejo complex (TPVC). The caldera's origin is controversial as both the formation by huge lateral flank collapse(s) and multiple vertical collapses have been proposed. Although vertical collapses may have facilitated lateral slope failures...

Université de Neuchâtel

Identification of zones of preferential groundwater tracer transport using a mobile downhole fluorometer

Flynn, Raymond Matthew ; Schnegg, Pierre-André ; Costa, Roberto ; Mallen, German ; Zwahlen, François

In: Hydrogeology Journal, 2005, vol. 13, p. 366-377

A mobile downhole fluorometer was used to detect zones of preferential groundwater tracer transport into an observation well. Identification of such zones is not possible if individual samples are collected over the wells entire screened interval. Laboratory-based tests using the fluorometer, and a purpose-built apparatus demonstrated that the fluorometer could be used with tracers to...

Université de Neuchâtel

Electrical structure of the tectonically active Kalabsha Fault, Aswan, Egypt

Schnegg, Pierre-André ; Arafa-Hamed, Tarek ; Elathy, Essam ; Mekkawi, Mahmoud

In: Earth and Planetary Science Letters, 2005, vol. 240, p. 764-773

In this work, we use the magnetotelluric (MT) method to detect geoelectrical conductivity anomalies in the Earth's crust and link them to local seismic activity. This application affords the unusual opportunity to study the percolation of water from a lake into a fault system and its effect on the induced seismicity. MT measurements were carried out in the period range 0.0046–420 s at nine...