Long-period P waveform modeling of upper mantle phases in the West Mediterranean basin

Abstract

Long-period P waveforms of some Italian crustal earthquakes recorded at the WWSSN stations located in the Iberian Peninsula have been modeled to derive a 1D upper matle compressional velocity model. A technique based on the Cagniard-de Hoop method has been used to compute synthetic seismograms. Waveforms have first been computed for published velocity models referred to different tectonic provinces and compared with the data. A model that strongly improves the fits to the data is then presented. The proposed model, called WMP, is characterized by a 100 km thick lid overlaying a low velocity zone, a 1% velocity discontinuity located at 313 km depth, that is required to fit a lower amplitude phase, and an abrupt increase in the velocity gradient starting from 370 km. This latter is preferred to the sharp discontinuity located at about 400 km that is present in various models obtained for upper mantle structure with analogous techniques. Within the lid and the low-velocity zone, WMP displays features that are typical of old ocean structures like the Northwest Atlantic Ocean.