Geodetic methods for detecting volcanic unrest: a theoretical approach

Abstract

In this paper we study the application of different geodetic techniques to volcanic activity monitoring, using theoretical analysis. This methodology is very useful for obtaining an idea of the most appropriate (and efficient) monitoring method, mainly when there are no records of geodetic changes previous to volcanic activity. The analysis takes into account the crustal structure of the area, its geology, and its known volcanic activity to estimate the deformation and gravity changes that might precede eruptions. The deformation model used includes the existing gravity field and vertical changes in the crustal properties. Both factors can have a considerable effect on computed deformation and gravity changes. Topography should be considered when there is a steep slope (greater than 107). The case study of Teide stratovolcano (Tenerife, Canary Islands), for which no deformation or gravity changes are available, is used as a test. To avoid considering topography, we worked at the lowest level of Las Cañ adas and examined a smaller area than the whole caldera or island. Therefore, the results are only a first approach to the most adequate geodetic monitoring system. The methodology can also be applied to active areas where volcanic risk is not associated with a stratovolcano but instead with monogenetic scattered centers, especially when sites must be chosen in terms of detection efficiency or existing facilities. The Canary Islands provide a good example of this type of active volcanic areas, and we apply our model to the island of Lanzarote to evaluate the efficiency of the monitoring system installed at the existing geodynamic station. On this island topography is not important. The results of our study show clearly that the most appropriate geodetic volcano monitoring system is not the same for all different volcanic zones and types, and the particular properties of each volcano/zone must be taken into account when designing each system.

GPS Monitoring in the N-W Part of the Volcanic Island of Tenerife, Canaries, Spain: Strategy and Results

“…For the elastic parameters we could consider those determined by FERNA´NDEZ et al (1999). They give as properties for the 3.5 km of the crust in their cortical model (from 2 km over sea level to 1.5 km below it) a density of 2100 kg m )3 , and Lameṕ arameters k= 8AE10 9 Pa and l ¼ 7AE10 9 Pa.…”

Shear-wave Velocity Structure around Teide Volcano: Results Using Microtremors with the SPAC Method and Implications for Interpretation of Geodetic Results

“…In previous works, a layered crustal model for the Tenerife Island was used in deformation models (see e.g., FERNA´NDEZ and Dı´EZ, 1995;FERNA´NDEZ et al, 1999). It was based on the velocity model by BOSSHARD and MACFARLANE (1970) determined by seismic experiments.…”

A new approach to the monitoring of deformation on Lanzarote (Canary Islands): an 8-year radar perspective

“…Yet, defining the most suitable monitoring system is particularly difficult in this case because of the absence of recent activity, and it becomes even harder if future eruptions are not limited to a specific volcano, but to a wide, active volcanic region, as on Lanzarote. This is a typical case in which the volcanic monitoring system must be carefully designed (Fernández 1993;Fernández et al 1993Fernández et al , 1999Fernández and Rundle 1994;Fernández and Díez 1995).…”