GNGTS 2022 - Atti del 40° Convegno Nazionale

GNGTS 2022 Sessione 1.2 113 receiving station. Several techniques have been developed in order to isolate the effects of the local structure beneath the observation point from others (e.g. source function and path effects) and to translate this information into models for the crust. Some methods involve the modelling of the crustal structure beneath the observation point using synthetic seismograms for P and SV waves. These techniques imply the comparison between synthetics and observed data to obtain the best fit and can be applied to deep or intermediate earthquakes, since the incident time function of such events can be often modelled as a single unidirectional pulse. If data of deep or intermediate events are not available, before applying synthetic seismograms calculation, the observed data must be equalized to compensate for different source time functions. A method to equalize the data is the receiver functions technique. This technique, first proposed by Langston (1979), allows, removing source and path-effects, to identify converted and reverberated phases in the crust generated by the interaction of a teleseismic P wave with a discontinuity surface in the crust. Precise information on the deep crustal and upper mantle structure beneath a single three-component broadband seismograph can be obtained basing on the assumption that the vertical component of a teleseismic event contains undesired source and path effects and is not significantly contaminated by the near receiver structure. Here we show a preliminary data analyses performed on teleseismic events recorded at MEFA station, a stand-alone seismic station equipped with a Guralp CMG40T 60s broadband sensor installed close to the Mefite emission vent on November 20, 2020, and at permanent seismic stations of the National and Irpinia Seismic Networks, located within 30 km away from Mefite vent and equipped with broadband sensors (Fig. 1). As a first step we considered the telesismic events with M > 6.5 recorded at MEFA and RSF3 station. The latter is part of the Irpina Network and it is located about 3.6 km from MEFA (Figure 1). After visual inspection of the seismograms in the time domain, those showing strongly impulsive onset were selected. Considering that the seismic stations are equipped with broadband sensors having different frequency response, the signals of each station have been deconvolved for their own frequency response to perform a first equalization of the data. Figure 2 shows an example of telesismic event recorded at MEFA and RSF3 stations. Although this event is not characterized by strongly impulsive onset, the similarity between the components is very evident. Fig. 2 - Example of teleseismic event recorder at MEFA and RSF3 stations. The seismograms are related to the event occurred in North Island, New Zealand: origin time 2020/03/04 13:27, hypocenter coordinates -37.0270° N, 179.4200° E, h=14 km b.s.l., Mw = 7.3. The seismograms are equalized taking into account that the sensors have different frequency response. The station name and the component are indicated for each trace.