Stefano Gresta - Academia.edu (original) (raw)

Papers by Stefano Gresta

In this paper we describe SHAKYGROUND, a software tool that has been designed with the aim of pro... more In this paper we describe SHAKYGROUND, a software tool that has been designed with the aim of providing the user a friendly environment allowing the simulation of strong ground motion by means of synthetic simulation of acceleration seismograms and the estimation of seismic load in a given area.

We studied site effects in the urban area of Ragusa-Ibla (South-eastern Sicily, Italy) by followi... more We studied site effects in the urban area of Ragusa-Ibla (South-eastern Sicily, Italy) by following some integrated different approaches. This city is located on an elongated and almost flat calcarenite hill in the south easternmost part of the Hyblean plateau. This region was struck in historical times by destructive to moderate earthquakes (i.e. 1169, 1542, 1693). As a first, we have performed a geological survey of the urban area (less than 1 km) at the scale 1:2000 collecting all geological and geotechnical available data from drillings. A further step of the study consisted in the application of the horizontal-to-vertical spectral ratio (HVSR) technique to microtremor measurements carried out at the ground surface of 40 sites. The results have evidenced significant variations of the frequency-amplitude response as a function of the site, in the frequency range 1-10 Hz. In particular, strong amplification is observed at sites located: i) on layers of “discarded material” (the ru...

During the COVID-19 pandemic, most countries worldwide put in place social interventions, consist... more During the COVID-19 pandemic, most countries worldwide put in place social interventions, consisting of restricting the mobility of citizens, aimed at slowing and mitigating the spread of the epidemic. In particular, Italy, as the first European country violently struck by the COVID-19 outbreak, applied a sequence of progressive restrictions to reduce both human mobility and human-to-human contacts from the end of February to mid-March 2020. Here, we analysed the seismic signatures of these lockdown measures in the densely populated Eastern Sicily, characterised by the presence of a permanent seismic network used for both seismic and volcanic monitoring. We specifically emphasize how the amount of the amplitude reduction of anthropogenic seismic noise (reaching ~50-60%), its temporal pattern and spectral content are strongly stationdependent. As for the latter, we exhibited that on average the frequencies above 10 Hz are the most influenced by the anthropogenic seismic noise. Finally, we found an impressive similarity between the temporal patterns of anthropogenic seismic noise and human mobility, as quantified by the mobile phone-derived data shared by Google, Facebook and Apple. These results further confirm how seismic data, routinely acquired worldwide for seismic and volcanic surveillance, can be used to monitor human mobility too.

Frontiers in Earth Science

In this work, we investigated the microseism recorded by a network of broadband seismic stations ... more In this work, we investigated the microseism recorded by a network of broadband seismic stations along the coastline of Eastern Sicily. Microseism is the most continuous and ubiquitous seismic signal on Earth and is mostly generated by the ocean-solid earth interaction. On the basis of spectral content, it is possible to distinguish three types of microseism: primary, secondary, and short-period secondary microseism (SPSM). We showed how most of the microseism energy recorded in Eastern Sicily is contained in the secondary and SPSM bands. This energy exhibits strong seasonal patterns, with maxima during the winters. By applying array techniques, we observed how the SPSM sources are located in areas of extended shallow water depth: the Catania Gulf and a part of the Northern Sicily coastlines. Finally, by using the significant wave height data recorded by two buoys installed in the Ionian and Tyrrhenian Seas, we developed an innovative method, selected among up-to-date machine learning techniques (MLTs), able to reconstruct the time series of sea wave parameters from microseism recorded in the three microseism period bands by distinct seismic stations. In particular, the developed model, based on random forest regression, allowed estimating the significant wave height with a low average error (∼0.14-0.18 m). The regression analysis suggests that the closer the seismic station to the sea, the more information concerning the sea state are contained in the recorded microseism. This is particularly important for the future development of an experimental monitoring system of the sea state conditions based on microseism recordings.

Remote Sensing

Global warming is making extreme wave events more intense and frequent. Hence, the importance of ... more Global warming is making extreme wave events more intense and frequent. Hence, the importance of monitoring the sea state for marine risk assessment and mitigation is increasing day-by-day. In this work, we exploit the ubiquitous seismic noise generated by energy transfer from the ocean to the solid earth (called microseisms) to infer the sea wave height data provided by hindcast maps. To this aim, we use a combined approach based on statistical analysis and machine learning. In particular, a random forest model shows very promising results in the spatial and temporal reconstruction of sea wave height by microseisms. The observed dependence of input importance from the distance sea grid cell-seismic station suggests how the reliable monitoring of the sea state in a wide area by microseisms needs data recorded by dense networks, comprising stations evenly distributed along the coastlines.

Mineralogical Magazine

An interdisciplinary approach for a new lithospheric model for southeastern Sicily and the Sicily... more An interdisciplinary approach for a new lithospheric model for southeastern Sicily and the Sicily Channel has been recently proposed by Manuella et al. [1], as retrieved from the integration of published petrologic and geophysical data. The model elaborated by Manuella et al. [1] points out the existence of a Permo-Triassic oceanic lithosphere that broadens from the Hyblean Plateau to the Sicily Channel, underlying a thick Mesozoic-Cenozoic sedimentary and volcanic sequence, in continuity with the adjacent Mesozoic Ionian-Tethys ocean, thus confirming the hypothesis of Scribano et al. [2]. The Permo-Triassic basement consists of a level of peridotites, affected by different degrees of serpentinization (35–100 vol.%) ranging to a depth of 8–19 km, and a remarkable anomaly occurs at 19 km, corresponding to the Moho discontinuity, which has been considered as a serpentinization front.

Tectonic stress in the Pacific Northwest Washington is dominated by a N-S major compressive axis ... more Tectonic stress in the Pacific Northwest Washington is dominated by a N-S major compressive axis s1 and a minor compressive axis s3 which varies from E-W to near vertical. Minor variations in this pattern occur in different parts of the region. In this study we used ca. 550 earthquakes in the central Washington Cascade Mountains to study in detail the uniformity of the stress tensor in this volcanic arc. Earthquakes from the Pacific Northwest Seismograph Network (PNSN) catalogue were divided into several subsets based on epicentral and depth groupings and stress-tensor inversions using the Gephart and Forsyth technique were computed for each group. As in previous similar studies the maximum compressive stress axis (s1) is nearly horizontal and trending ca. N-S and NNE-SSW in all but one subset. Shallower events directly under Mount Rainier have a near vertical s1. For other subsets the minimum compressive stress axis (s3) deviates from vertical to horizontal for different groups of ...

The seismic network set up in the Iblean Plateau (Southeastern Sicily) in the framework of the PO... more The seismic network set up in the Iblean Plateau (Southeastern Sicily) in the framework of the POSEIDON project is aimed at the seismic surveillance of the zone, and in particular the identification of faults with enhanced activity. The seismic activity as inferred from the records of local events recorded in the time span September 1999-February 2000 showed an apparent concentration of events in the zone between Augusta and Siracusa. However, the heterogeneity in the distribution of events with daytime suggested that the seismicity maps are severely biased by artificial events, such as quarry explosions. We have distinguished between tectonic earthquakes and quarry blasts by the inspection of waveforms of certain key stations, and by spectral analysis. As a general rule we found that the local tectonic microearthquakes are richer in high frequencies than the quarry blasts. We tested our discrimination based on waveforms and spectra with a data of local events recorded in the time s...

Introduction. The Dead Sea Fault System (DSFS) represents the left-lateral transform boundary bet... more Introduction. The Dead Sea Fault System (DSFS) represents the left-lateral transform boundary between the Arabian and Sinai plates (e.g. Jackson and McKenzie, 1988), stretching from the Red Sea mid-oceanic ridge to the south, to the Bitlis-Zagros (southern Turkey) continental collision zone to the north, where the DSFS joins with the East Anatolian fault (EAF; Fig. 1a). The DSFS is generally subdivided into three sections (Fig. 1b). The southern section, extending from the Gulf of Aqaba (Red Sea) through the Jordan Valley, is characterized by the presence of predominantly leftlateral strike-slip faults striking between N12°E and N20°E, having a small component of extension in the south (Gulf of Aqaba) and increasing compression toward the north (

Pure and Applied Geophysics, 2014

The aim of this work was to investigate the seismic attenuation of the medium in the uppermost 5 ... more The aim of this work was to investigate the seismic attenuation of the medium in the uppermost 5 km of the crust at Mt. Etna volcano. We selected ca. 270 shallow microearthquakes (2.6<Ml<3.0) recorded during two episodes of intense seismic activity which preceded and accompanied the two most recent eruptions at Mt. Etna occurred in 2001 and 2002. The quality

ABSTRACT Recent studies showed the occurrence of non-volcanic tremor in the Cascadia Subduction z... more ABSTRACT Recent studies showed the occurrence of non-volcanic tremor in the Cascadia Subduction zone, in the southwest Japan and along the San Andreas Fault. In the southwest Japan the non-volcanic tremor was accompanied by low-frequency earthquakes (LFEs). Using a method developed on tremor at Mt. Etna volcano, we apply a detection procedure to look for LFEs in the non-volcanic tremor recorded during 2004-2006 along the San Andreas Fault, by a seismic network comprising 13 3-C stations. This method is composed of two steps, trigger detection and trigger selection. The former is based on three algorithms, standard, adaptive standard and adaptive recursive STA/LTA, that evaluate the ratio between short- and long-term energy density to find amplitude transients. The main differences between them consist in the manual or automatic (adaptive) selection of the window length of the STA and LTA and in the rectangular or decaying exponential impulse response (standard and recursive, respectively). Using these algorithms we obtain a trigger list for each station. Trigger selection consists of selecting from these lists the triggers common at many of the stations which are characterised by similar spectral content of the seismic signal following the triggers and a time distribution of triggers consistent with the distribution of the stations. Applying this procedure we were able to find small amplitude transients related to LFE activity.

Modeling of Volcanic Processes, 1988

Tectonophysics, 1990

The differing behaviour of the eastern and western flanks of Mount Etna has been investigated by ... more The differing behaviour of the eastern and western flanks of Mount Etna has been investigated by analyzing morphological, structural, volcanic and seismic data. Morphological and structural analyses have pointed out a higher "degree" of tectonization on the eastern side. From the volcanoiogical point of view, the analysis of some parameters of adventive eruptions during the last three centuries did not evidence great differences between the two sides of the volcano. only higher lava outputs on the eastern flank have been remarked. Historic and recent seismic activity has been analyzed for the number and magnitude of events, strain energy release and frequency-magnitude law. The shallowest and strongest earthquakes occur on the eastern side of the volcano, strictly linked to a regional structural system trending NNW-SSE. The western side is mostly characterized by deeper earthquakes that seem to control the volcanic activity. Lower seismic energy releases and higher values of the b coefficient in the Gutenberg-Richter's (1956) law can be observed on the western side. The differences observed between the two sides of the volcano have been interpreted in terms of both regional and local tectonics, with the result that a higher extensional stress field is attributed to the eastern side of the volcano.

In this paper we describe SHAKYGROUND, a software tool that has been designed with the aim of pro... more In this paper we describe SHAKYGROUND, a software tool that has been designed with the aim of providing the user a friendly environment allowing the simulation of strong ground motion by means of synthetic simulation of acceleration seismograms and the estimation of seismic load in a given area.

We studied site effects in the urban area of Ragusa-Ibla (South-eastern Sicily, Italy) by followi... more We studied site effects in the urban area of Ragusa-Ibla (South-eastern Sicily, Italy) by following some integrated different approaches. This city is located on an elongated and almost flat calcarenite hill in the south easternmost part of the Hyblean plateau. This region was struck in historical times by destructive to moderate earthquakes (i.e. 1169, 1542, 1693). As a first, we have performed a geological survey of the urban area (less than 1 km) at the scale 1:2000 collecting all geological and geotechnical available data from drillings. A further step of the study consisted in the application of the horizontal-to-vertical spectral ratio (HVSR) technique to microtremor measurements carried out at the ground surface of 40 sites. The results have evidenced significant variations of the frequency-amplitude response as a function of the site, in the frequency range 1-10 Hz. In particular, strong amplification is observed at sites located: i) on layers of “discarded material” (the ru...

During the COVID-19 pandemic, most countries worldwide put in place social interventions, consist... more During the COVID-19 pandemic, most countries worldwide put in place social interventions, consisting of restricting the mobility of citizens, aimed at slowing and mitigating the spread of the epidemic. In particular, Italy, as the first European country violently struck by the COVID-19 outbreak, applied a sequence of progressive restrictions to reduce both human mobility and human-to-human contacts from the end of February to mid-March 2020. Here, we analysed the seismic signatures of these lockdown measures in the densely populated Eastern Sicily, characterised by the presence of a permanent seismic network used for both seismic and volcanic monitoring. We specifically emphasize how the amount of the amplitude reduction of anthropogenic seismic noise (reaching ~50-60%), its temporal pattern and spectral content are strongly stationdependent. As for the latter, we exhibited that on average the frequencies above 10 Hz are the most influenced by the anthropogenic seismic noise. Finally, we found an impressive similarity between the temporal patterns of anthropogenic seismic noise and human mobility, as quantified by the mobile phone-derived data shared by Google, Facebook and Apple. These results further confirm how seismic data, routinely acquired worldwide for seismic and volcanic surveillance, can be used to monitor human mobility too.

Frontiers in Earth Science

In this work, we investigated the microseism recorded by a network of broadband seismic stations ... more In this work, we investigated the microseism recorded by a network of broadband seismic stations along the coastline of Eastern Sicily. Microseism is the most continuous and ubiquitous seismic signal on Earth and is mostly generated by the ocean-solid earth interaction. On the basis of spectral content, it is possible to distinguish three types of microseism: primary, secondary, and short-period secondary microseism (SPSM). We showed how most of the microseism energy recorded in Eastern Sicily is contained in the secondary and SPSM bands. This energy exhibits strong seasonal patterns, with maxima during the winters. By applying array techniques, we observed how the SPSM sources are located in areas of extended shallow water depth: the Catania Gulf and a part of the Northern Sicily coastlines. Finally, by using the significant wave height data recorded by two buoys installed in the Ionian and Tyrrhenian Seas, we developed an innovative method, selected among up-to-date machine learning techniques (MLTs), able to reconstruct the time series of sea wave parameters from microseism recorded in the three microseism period bands by distinct seismic stations. In particular, the developed model, based on random forest regression, allowed estimating the significant wave height with a low average error (∼0.14-0.18 m). The regression analysis suggests that the closer the seismic station to the sea, the more information concerning the sea state are contained in the recorded microseism. This is particularly important for the future development of an experimental monitoring system of the sea state conditions based on microseism recordings.

Remote Sensing

Global warming is making extreme wave events more intense and frequent. Hence, the importance of ... more Global warming is making extreme wave events more intense and frequent. Hence, the importance of monitoring the sea state for marine risk assessment and mitigation is increasing day-by-day. In this work, we exploit the ubiquitous seismic noise generated by energy transfer from the ocean to the solid earth (called microseisms) to infer the sea wave height data provided by hindcast maps. To this aim, we use a combined approach based on statistical analysis and machine learning. In particular, a random forest model shows very promising results in the spatial and temporal reconstruction of sea wave height by microseisms. The observed dependence of input importance from the distance sea grid cell-seismic station suggests how the reliable monitoring of the sea state in a wide area by microseisms needs data recorded by dense networks, comprising stations evenly distributed along the coastlines.

Mineralogical Magazine

An interdisciplinary approach for a new lithospheric model for southeastern Sicily and the Sicily... more An interdisciplinary approach for a new lithospheric model for southeastern Sicily and the Sicily Channel has been recently proposed by Manuella et al. [1], as retrieved from the integration of published petrologic and geophysical data. The model elaborated by Manuella et al. [1] points out the existence of a Permo-Triassic oceanic lithosphere that broadens from the Hyblean Plateau to the Sicily Channel, underlying a thick Mesozoic-Cenozoic sedimentary and volcanic sequence, in continuity with the adjacent Mesozoic Ionian-Tethys ocean, thus confirming the hypothesis of Scribano et al. [2]. The Permo-Triassic basement consists of a level of peridotites, affected by different degrees of serpentinization (35–100 vol.%) ranging to a depth of 8–19 km, and a remarkable anomaly occurs at 19 km, corresponding to the Moho discontinuity, which has been considered as a serpentinization front.

Tectonic stress in the Pacific Northwest Washington is dominated by a N-S major compressive axis ... more Tectonic stress in the Pacific Northwest Washington is dominated by a N-S major compressive axis s1 and a minor compressive axis s3 which varies from E-W to near vertical. Minor variations in this pattern occur in different parts of the region. In this study we used ca. 550 earthquakes in the central Washington Cascade Mountains to study in detail the uniformity of the stress tensor in this volcanic arc. Earthquakes from the Pacific Northwest Seismograph Network (PNSN) catalogue were divided into several subsets based on epicentral and depth groupings and stress-tensor inversions using the Gephart and Forsyth technique were computed for each group. As in previous similar studies the maximum compressive stress axis (s1) is nearly horizontal and trending ca. N-S and NNE-SSW in all but one subset. Shallower events directly under Mount Rainier have a near vertical s1. For other subsets the minimum compressive stress axis (s3) deviates from vertical to horizontal for different groups of ...

The seismic network set up in the Iblean Plateau (Southeastern Sicily) in the framework of the PO... more The seismic network set up in the Iblean Plateau (Southeastern Sicily) in the framework of the POSEIDON project is aimed at the seismic surveillance of the zone, and in particular the identification of faults with enhanced activity. The seismic activity as inferred from the records of local events recorded in the time span September 1999-February 2000 showed an apparent concentration of events in the zone between Augusta and Siracusa. However, the heterogeneity in the distribution of events with daytime suggested that the seismicity maps are severely biased by artificial events, such as quarry explosions. We have distinguished between tectonic earthquakes and quarry blasts by the inspection of waveforms of certain key stations, and by spectral analysis. As a general rule we found that the local tectonic microearthquakes are richer in high frequencies than the quarry blasts. We tested our discrimination based on waveforms and spectra with a data of local events recorded in the time s...

Introduction. The Dead Sea Fault System (DSFS) represents the left-lateral transform boundary bet... more Introduction. The Dead Sea Fault System (DSFS) represents the left-lateral transform boundary between the Arabian and Sinai plates (e.g. Jackson and McKenzie, 1988), stretching from the Red Sea mid-oceanic ridge to the south, to the Bitlis-Zagros (southern Turkey) continental collision zone to the north, where the DSFS joins with the East Anatolian fault (EAF; Fig. 1a). The DSFS is generally subdivided into three sections (Fig. 1b). The southern section, extending from the Gulf of Aqaba (Red Sea) through the Jordan Valley, is characterized by the presence of predominantly leftlateral strike-slip faults striking between N12°E and N20°E, having a small component of extension in the south (Gulf of Aqaba) and increasing compression toward the north (

Pure and Applied Geophysics, 2014

The aim of this work was to investigate the seismic attenuation of the medium in the uppermost 5 ... more The aim of this work was to investigate the seismic attenuation of the medium in the uppermost 5 km of the crust at Mt. Etna volcano. We selected ca. 270 shallow microearthquakes (2.6<Ml<3.0) recorded during two episodes of intense seismic activity which preceded and accompanied the two most recent eruptions at Mt. Etna occurred in 2001 and 2002. The quality

ABSTRACT Recent studies showed the occurrence of non-volcanic tremor in the Cascadia Subduction z... more ABSTRACT Recent studies showed the occurrence of non-volcanic tremor in the Cascadia Subduction zone, in the southwest Japan and along the San Andreas Fault. In the southwest Japan the non-volcanic tremor was accompanied by low-frequency earthquakes (LFEs). Using a method developed on tremor at Mt. Etna volcano, we apply a detection procedure to look for LFEs in the non-volcanic tremor recorded during 2004-2006 along the San Andreas Fault, by a seismic network comprising 13 3-C stations. This method is composed of two steps, trigger detection and trigger selection. The former is based on three algorithms, standard, adaptive standard and adaptive recursive STA/LTA, that evaluate the ratio between short- and long-term energy density to find amplitude transients. The main differences between them consist in the manual or automatic (adaptive) selection of the window length of the STA and LTA and in the rectangular or decaying exponential impulse response (standard and recursive, respectively). Using these algorithms we obtain a trigger list for each station. Trigger selection consists of selecting from these lists the triggers common at many of the stations which are characterised by similar spectral content of the seismic signal following the triggers and a time distribution of triggers consistent with the distribution of the stations. Applying this procedure we were able to find small amplitude transients related to LFE activity.

Modeling of Volcanic Processes, 1988

Tectonophysics, 1990

The differing behaviour of the eastern and western flanks of Mount Etna has been investigated by ... more The differing behaviour of the eastern and western flanks of Mount Etna has been investigated by analyzing morphological, structural, volcanic and seismic data. Morphological and structural analyses have pointed out a higher "degree" of tectonization on the eastern side. From the volcanoiogical point of view, the analysis of some parameters of adventive eruptions during the last three centuries did not evidence great differences between the two sides of the volcano. only higher lava outputs on the eastern flank have been remarked. Historic and recent seismic activity has been analyzed for the number and magnitude of events, strain energy release and frequency-magnitude law. The shallowest and strongest earthquakes occur on the eastern side of the volcano, strictly linked to a regional structural system trending NNW-SSE. The western side is mostly characterized by deeper earthquakes that seem to control the volcanic activity. Lower seismic energy releases and higher values of the b coefficient in the Gutenberg-Richter's (1956) law can be observed on the western side. The differences observed between the two sides of the volcano have been interpreted in terms of both regional and local tectonics, with the result that a higher extensional stress field is attributed to the eastern side of the volcano.