Characterization of volcanic materials using shallow geophysical techniques: 2. Ground penetrating radar

We have analyzed the ground penetrating radar (GPR) response in several volcanic materials (massive, pahoehoe and aa lava flows and airfall deposits) occurring in the Las Cañadas edifice (Tenerife, Canary Islands), in order to recognize their occurrence and characterize their thickness, spatial distribution, internal structures and discontinuities, as well as to evaluate the mean velocities of the electromagnetic waves in these rocks and deposits. The obtained GPR profiles show that, depending on the nature of the materials, the geometry of the reflectors is distinctive. The GPR reflectors of airfall pumice are thin, well-layered and laterally continuous. In contrast, different lava flows originate a different radar response. Regarding the pahoehoe lava flows, their radar signature is characterized by well defined reflectors. The aa lava flows exhibit weak reflectors. Massive lava flows are resolved as homogeneous structures with scarce or absent internal reflections. The mean velocity of the electromagnetic waves through the different deposits ranges from 0.07 to 0.099 m·ns-1. As a general approximation, the velocity of the electromagnetic waves is faster in lava flows that in airfall deposits, where attenuation is greater and penetration depth is lower. The estimation of the propagation velocity for the electromagnetic waves has allowed us to process the profiles and to carry out depth-time conversions and migration, in order to get more realistic 2-D representation