IGCP 565 Workshop 3: Separating Hydrological and Tectonic Signals in Geodetic Observations Reno, Nevada, October 11-13, 2010

B2: Separation of signals on micro to river basin scales

Co-Conveners: Michel Van Camp (Royal Observatory of Belgium), Charles Meertens (UNAVCO), Shimon Wdowinski (RSMAS, University of Miami), Ty Ferre (University of Arizona)

Geodetic quantities integrate many phenomena, and it remains a challenge to separate the contribution from the different sources, in our case tectonic and hydrological signals. This can only be achieved by two different ways: (1) if the two sources have deeply different space/time signature, they can be separated using numerical processing methods, (2) if it is possible to determine one of the sources by any other observation/modelling techniques, it can be subtracted to isolate the other one.

The increasing accuracies of space geodetic techniques enable the detection of small surface changes over large areas. Apparent geodetic changes are the result of tectonic, hydrologic, atmospheric and other processes. Therefore, understanding the significance of the measured signal can be challenging and requires a multidisciplinary effort.

In particular, land-based gravity measurements are very sensitive to local water storage changes (WSC). Consequently, at the local scale, in many areas, the hydrological signal dominates the measured gravimetric signal, after the classical correction for tidal, atmospheric and polar motion effects. The gravimetric signature of the WSC depends on very local geologic and climatic conditions, e.g. rock porosity, vegetation, evaporation, and runoff rates; this signature can be more important than any tectonic effects and may induce large time correlated noise into the data.

On the other hand, observable ground deformations are usually associated with larger scale WSC. Nevertheless, in some particular conditions, tilts and deformations can be observed at the local scale, for example in the vicinity of hydrothermal and volcanic systems or on locations undergoing anthropogenic uplift/subsidence due to mass withdrawal/injection or surface loading from lakes.

This session will consider geodetic signals at spatial scales from several meters and up to river basin scales (> tens of kilometers) resulting from tectonic and hydrological processes. We will discuss the fingerprints of tectonic and hydrological signals at these scales in geodetic observations.

At river-basin scales we will consider basins located within active plate boundary regions, where tectonic processes form the large-scale landforms, surface and hydrological processes shape the landscape, and subsurface water storage changes on seasonal and longer periods. These larger-scale basins are located along active mountain belts, such as the Ganges Basins, which drains the southern Himalayas. Smaller- and intermediate-scale basins are located within transcurrent and divergent plate boundaries, in which their segmented nature gives rise to variable scale landforms.

The session will include observations from several basins in Asia, the western U.S., the eastern Mediterranean, and possibly other regions where both tectonic and hydrological signals affect geodetic observations. We will discuss the level to which these signals can be separated as well as uncertainties in the separation. Emphasis will be placed on the causes of uncertainties and methods to reduce them. Finally, we will evaluate how anthropogenic impacts on hydrological processes can act as a source of interpretation error and, simultaneously, offers an opportunity for environmental monitoring.