Franco Pettenati

A small, isolated portion of Marmolada Glacier broke off on 3 July 2022. The detached ice mass had an estimated volume of 70 400 m³ and slid down the slope, killing 11 mountaineers after having traveled for approximately 2.3 km along the northern slope. This event is considered among the deadliest ice avalanches historically recorded in the Alps. The unusually high air temperatures in late spring and early summer of that year led to an excess of meltwater, which, since mid-June, had overpressurized the englacial discharge network, partly blocked due to frozen conditions at its base. Ice temperature, subglacial permafrost and heat exchange from meltwater were among the primary factors controlling the thermal state of the sliding surface. The cause of the collapse was investigated by exploiting a conceptual model that was further corroborated through simplified numerical simulations using the limit equilibrium method. Pre- and post-failure satellite and aerial images, laser mapping, and geophysics and morpho-climatic data were gathered in a comprehensive database and analyzed to better understand the role and interaction of the predisposing and triggering factors as well as their mutual interaction. Particular attention was given to reconstructing the varying conditions of the failure surface, which developed partly along ice foliations near the glacieret's base and partly right at the ice–bedrock interface. An earthquake triggering the failure was excluded based on the processing of the available seismological observations. It transpired that none of the three forces considered in the numerical analysis – namely, hydrostatic pressure in crevasses, hydraulic jacking and basal friction reduction – individually caused the condition of instability. To reach this condition, it was necessary to invoke a combination of these actions, for which it was finally possible to estimate their relative weights.

We present an overview of the inversions performed with the KF method (Pettenati and Sirovich 2003; Sirovich and Pettenati 2004) on some historical earthquakes in the CPTI15 catalogue data domain. This method is based on a kinematic function (KF) that is controlled during the inversion by the Genetic Algorithm with Niching's Variant (NGA) algorithm (Gentile et al. 2004).Since we are dealing with historical earthquakes, a distinction is first made between instrumental and pre-instrumental earthquakes. For the former between 1900 and 2009 a quantitative assessment is made, for the latter only qualitative assessments can be made. We present statistics to evaluate the magnitude and epicentral coordinates obtained from KF with instrumental data or the parameters of the CPTI15 catalogue. To evaluate the fault plane solutions, we instead used the disorientation angles with the instrumental focal mechanisms (Sirovich et al. 2013). In the case of pre-instrumental earthquakes, the assessments vary from case to case. From the comparison of the results obtained with techniques based on the conversion of strong motion data into intensity, statistical analysis or comparison with the seismotectonic of the area could be made.ReferencesGentile, F., F., Pettenati and Sirovich, L.; 2004. Validation of the Automatic Nonlinear Source Inversion of the U. S. Geological Survey Intensities of the Whittier Narrows, 1987 Earthquake. Bull. Seism. Soc. Am., vol.94, No.5, 1737-1747, October 2004, https://doi.org/10.1785/012003157.Pettenati, F., and Sirovich, L.; 2003. Test of Source-Parameter Inversion of the USGS Intensities of the Whittier Narrows, 1987 earthquake. Bull. Seism. Soc. Am, vol.93, No.1, 47-60, February 2003, https://doi.org/10.1785/0120010113.Sirovich, L. and. Pettenati, F; 2004. Source Inversion of Intensity patterns of Earthquakes; a Destructive Shock in 1936 in northeast Italy. Journal of Geophysical Research, vol. 109, B10309, 2004, 1-16, https://doi.org/10.1029/2003JB002919.

Macroseismic intensity data are the only source of information for historical earthquakes; it is therefore necessary to devise methods that allow us to retrieve as many source parameters as possible on the basis of these data. We present the inversion of macroseismic data as a first validation of an improved version of the kinematic function, KF. Following the previous results of some earthquakes on Italian territory and several validations by Californian events provided with instrumental solutions, we have now simplified the KF by reducing some degrees of freedom of the parameters and rearranging the code for parallel calculation. This approach will allow for a more extensive application of the KF technique. We present the inversion of the macroseismic intensity pattern of the M_wp6 earthquake of 27 March 1928 (8:32 GMT), which occurred in Northeastern Italy (Carnia), and we retrieved source parameters that are compatible with the solutions of other authors who independently treat instrumental data. The 1928 event is located a few tens of kilometers west of the more destructive M_w6.5 of 6 May 1976 and northeast of the subsequent earthquake M_wp6.1 of 18 October 1936. The inversion was performed as a blind test, without prior knowledge for fault plane solutions and tectonic information; it resulted in a minimum variance model with a strike of 62°, a dip of 10°, and a rake of 101°. This solution is not consistent with the entire tectonic framework of the eastern Southalpine chain, but it is in agreement with the But-Chiarsò line. This result encourages us to test further improvements to the KF method and to treat other cases from the Italian macroseismic catalog.

This article presents an overview of the first 10 yr of activity of the IO.EVN seismographic broadband station, managed by the Istituto Nazionale di Oceanografia e di Geofisica Sperimentale - OGS and installed near the Observatory-Laboratory Pyramid, about 6 km from Everest Base Camp (Nepal) at 5000 m above sea level. The IO.EVN station is registered in the International Federation of Digital Seismograph Networks (FDSN; see Data and Resources). It has been in operation since 2014 and played a crucial role during the 2015 crisis following the Gorkha earthquake because it was the closest broadband seismometer to the epicenter. The site is located in a remote area with ideal conditions for noise attenuation and is suitable for recording environmental microtremors and earthquakes in the Himalayas and worldwide. Khumbu Valley (Mount Everest) is one of the Himalayan regions that has not been struck by significant earthquakes (Mw > 7.8) in living memory. Although the analysis of microseismicity deserves further investigation, this article focuses more on the analysis of seismic noise, which was conducted to identify the various weather and climate phenomena affecting the region. In our case, we have found that for the major weather phenomena such as typhoons the main effect is due to the reflection of ocean waves on the coasts, whereas local effects such as rain and wind during the monsoon are more significant as the noise level of waves is probably constant throughout the year. The Pyramid is an important station for weather and climate, and the role of the IO.EVN could prove relevant in understanding climate change in the future.

A small, isolated portion of the Marmolada glacier partially broke off on July 3, 2022. The detached ice mass had an estimated volume of 70,400 m³ and slid down the slope killing 11 mountaineers after having travelled for approximately 2.3 km along the northern slope. This event is considered among the deadliest ice avalanches historically recorded in the Alps. The cause of the collapse is most likely to be closely related to anomalously high air temperatures in late spring and early summer of that year and also to progressive warming of basal ice layers and subglacial permafrost. Increased melting resulted in significant amounts of water that could not be discharged but remained trapped in crevasses of the isolated, cold ice body. The usually high permeability of karst systems in limestone are likely to have been blocked by subglacial and surrounding permafrost rocks, thereby increasing basal water pressure. Morpho-climatic data, satellite and aerial images and geophysics were analysed to better understand role and interaction of the controlling factors. This enabled the implementation of a conceptual model that was further investigated through numerical simulations using the Limit Equilibrium Method. The outcome from the back-analysis indicates that a combination of driving forces was required to finally trigger the collapse. The seasonal alternation of prolonged heating and refreezing meltwater of subglacial permafrost (i.e. the active layer) could have caused the plasticization of the basal ice resulting in the presence of a “weak bottom layer” where the available shear strength progressively dropped, finally triggering the failure.

The 14 April 1895 (Mw 6.1, in the area of Ljubljana, Slovenia) earthquake is still not fully understood. The aim of this work is to derive information about its source from the inversion of an updated dataset of intensities (evaluated with EMS-98). This was done via automatic non-linear geophysical inversion KF-NGA, which was performed using a Niching Genetic Algorithm and has been presented in other articles. The distribution of damage caused by this earthquake is not homogeneous and often shows significant intensity differences between neighbouring sites. Statistical analysis of the intensities, epicentral distances and geologic nature of the sites suggests some site effects. Nevertheless, the resulting solution is consistent with regional seismotectonics, i.e. an almost pure dip-slip mechanism: strike 282° ± 5°, dip 38° ± 7°, rake 86° ± 9° (± 180° because of the intrinsic ambiguity of the KF-NGA-inversion). Since the rake angle is close to 90°, there is an almost perfect ambiguity between the two planes of the focal mechanism. Therefore, our solution has a Dinaric direction and could be associated either with a fault plane that dips NE or with one that dips SW.

The 14 April 1895 earthquake (Mw 6.1, in the Ljubljana area, Slovenia) is still not fully explained. The aim of this paper is to derive information on its source from the inversion of an updated dataset of intensities (evaluated using EMS-98). This was done by the KF-NGA automatic non-linear geophysical inversion, with a Niching Genetic Algorithm technique, already presented in other articles. The distribution of damage caused by this earthquake is not homogeneous, often with significant differences of intensity between neighboring sites. The statistical analysis of intensities, epicentral distances and sites geology suggests some site effects. Despite this, the resulting solution is compatible with the regional seismotectonics, i.e. an almost pure dip-slip mechanism: strike angle 282°5°, dip 38°±7°, rake 86°±9° (±180° because of the intrinsic ambiguity of the KF-NGA inversion). Since the rake angle is close to 90°, there is an almost perfect ambiguity between the two planes of the focal mechanism. Thus, our solution has a Dinaric direction and could be associated with either a fault plane dipping NE or with one dipping SW.

SUMMARY: This research aims at characterizing the deep sedimentary basin of Kathmandu (Nepal) from microtremor measurements, by using two surveys carried out in November 2015 and November 2018. The data collected are sufficient for a qualitative investigation of the seismic response of such a complex basin. The measurements were undertaken in the framework of a collaboration between the NSET (National Society for Earthquake Technology, Nepal) and the OGS (National Institute of Oceanography and Applied Geophysics, Italy). During the two campaigns, a series of passive seismic surveys were made, taking into consideration both single broad-band sensors and arrays. The 2015 study initially focused on the Lalitpur area (southern part of Kathmandu) and was later extended to the northern and more urbanized area of the capital city of Nepal. The 2018 survey focused on estimating the S-wave velocity field of the entire stratigraphic sequence by array and a repetition of some Horizontal to Vertical Spectral Ratio (HVSR) measurements close to two boreholes with reliable stratigraphy. Two inversion methods, using the data from the seismic arrays, were useful to infer the S-wave velocity profiles of the shallower layers and to interpret some HVSRs. The outcome is a map of the periods of single station data representing the seismic response of the basin. Comparing these results with the strong motion data of the Gorkha 2015 main shock, we confirm that the longer periods are not only the effects of the earthquake source, but also of the local response of the basin itself.