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Wed 30 Oct 14:00: Water can move mountains: hydrologically induced deformation in the Apennines (Italy) and Sierra Nevada (California) observed from GNSS data

http://talks.cam.ac.uk/show/rss/15125 - Thu, 19/09/2024 - 12:20

Water can move mountains: hydrologically induced deformation in the Apennines (Italy) and Sierra Nevada (California) observed from GNSS data

The redistribution of water masses due to temporal variations of hydrological conditions can produce observable deformation of the shallow crust. Space geodetic techniques, such as GNSS , have provided a considerable improvement in terms of data accuracy and spatial and temporal resolution for the detection and investigation of this kind of deformation. In particular, in the areas where snow and water accumulate for long periods, such as mountainous areas and aquifers, relatively high deformation (up to several millimeters in the vertical and horizontal components) has been observed. In this work, we analyze two areas which are interesting from both hydrological and tectonic point of views. The Apennines represent one of the most seismic areas of Italy. The karst aquifers hosted in this mountain range are able to store huge quantities of groundwater and provide water supply for large cities like Rome and Naples. The Sierra Nevada provides most of California’s water supply and is located right next to a large and still active volcanic system that includes Long Valley Caldera. Combining displacement data from dense permanent GNSS networks with various hydrological records we analyze these two case-studies to deconvolve the transient, hydrological deformation from steady-state, tectonic deformation. We show that the karst aquifers of the Apennines deform in response to seasonal and interannual variations of groundwater content, producing a visible transient signal in the time series of the surrounding GNSS sites. This suggests that the large karst aquifers of this region alternately expand and contract in response to higher/lower groundwater content in the aquifers and, consequently to variable hydraulic head. Thanks to the availability of a dense GNSS network and different kinds of hydrological data we focus on the process causing the observed deformation. Sierra Nevada represents a geophysically complex area due to the presence of an active magmatic system, tectonic motion with associated seismicity and the hydrological forcing associated with the huge amount of precipitation that falls on the Sierra Nevada and its spatiotemporal variability. These superimposed tectonic and non-tectonic processes cause composite deformation including long-term tectonic motion, episodic inflation of the resurgent dome and variable seasonal and multi-year displacements from surface water loading and subsurface discharge/recharge. We observe a clear vertical deformation pattern whose spatiotemporal variability is likely related to surface loading acting both at the large (regional or continental) and local scales. We highlight anomalous horizontal deformation in the GNSS sites on the Sierra Nevada range front, showing its clear correlation with spring discharge. We investigate possible causes of this significant deformation, including response to snowpack loading and the influence of groundwater recharge.

Speaker: Francesca Silverii, Istituto Nazionale di Geofisica e Vulcanologia (INGV, Italy)
Wednesday 30 October 2024, 14:00-15:00
Venue: Wolfson Lecture Theatre.
Series: Bullard Laboratories Wednesday Seminars; organiser: Adriano Gualandi.

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