Seismic Source Classification by Means of a Sonogram- Correlation Approach: Application to Data of the RSM Seismic Network (Central Italy)

—?In this paper, we apply a new sonogram correlation approach for seismic source classification. In order to test the technique, we use the waveforms recorded by 6 among 16 of the stations of the Rete Sismometrica Marchigiana (RSM) network, relevant to the vertical component of 365 earthquakes that occurred in the analyzed area from April 1996 until September 1999. All the sonograms of each station are cross-correlated in a single station procedure and the calculated degrees of resemblance are used to classify the events by means of a bridging technique. The results obtained with the single-station approach are integrated into a network classification. We identified three families in the investigated area. Once the efficiency of the method is tested, we analyzed the families obtained for the selected subset of events. Considering the temporal and the spatial distribution of the events forming each family, we classified them as quarry blasts. This classification, even if relevant to a subset of earthquakes occurring in Central Italy, modifies the present knowledge of the seismicity distribution in the area and allows estimation of the errors affecting the hypocenter locations provided by the RSM network. An extension of this new technique to the whole Central Italy earthquake catalog promises an interesting review of the seismicity in the area.     

Locations and magnitudes of earthquakes in Central Asia from seismic intensity data

We apply the Bakun and Wentworth (Bull Seism Soc Am 87:1502–1521, 1997) method to determine the location and magnitude of earthquakes occurred in Central Asia using MSK-64 intensity assignments. The attenuation model previously derived and validated by Bindi et al. (Geophys J Int, 2013) is used to analyse 21 earthquakes that occurred over the period 1885–1964, and the estimated locations and magnitudes are compared to values available in literature. Bootstrap analyses are performed to estimate the confidence intervals of the intensity magnitudes, as well as to quantify the location uncertainty. The analyses of seven significant earthquakes for the hazard assessment are presented in detail, including three large historical earthquakes that struck the northern Tien-Shan between the end of the nineteenth and the beginning of the twentieth centuries: the 1887, M 7.3 Verny, the 1889, M 8.3 Chilik and the 1911, M 8.2 Kemin earthquakes. Regarding the 1911, Kemin earthquake the magnitude values estimated from intensity data are lower (i.e. MI_LH?=?7.8 and MI_W?=?7.6 considering surface wave and moment magnitude, respectively) than the value M?=?8.2 listed in the considered catalog. These values are more in agreement with the value M _S?=?7.8 revised by Abe and Noguchi (Phys Earth Planet In, 33:1–11, 1983b) for the surface wave magnitude. For the Kemin earthquake, the distribution of the bootstrap solutions for the intensity centre reveal two minima, indicating that the distribution of intensity assignments do not constrain a unique solution. This is in agreement with the complex source rupture history of the Kemin earthquake, which involved several fault segments with different strike orientations, dipping angles and focal mechanisms (e.g. Delvaux et al. in Russ Geol Geophys 42:1167–1177, 2001; Arrowsmith et al. in Eos Trans Am Geophys Union 86(52), 2005). Two possible locations for the intensity centre are obtained. The first is located on the easternmost sub-faults (i.e. the Aksu and Chon-Aksu segments), where most of the seismic moment was released (Arrowsmith et al. in Eos Trans Am Geophys Union 86(52), 2005). The second location is located on the westernmost sub-faults (i.e. the Dzhil'-Aryk segment), close to the intensity centre location obtained for the 1938, M 6.9 Chu-Kemin earthquake (MI_LH?=?6.9 and MI_W?=?6.8).