TY - JOUR A1 - Bindi, Dino A1 - Cotton, Fabrice Pierre A1 - Spallarossa, Daniele A1 - Picozzi, Matteo A1 - Rivalta, Eleonora T1 - Temporal variability of ground shaking and stress drop in Central Italy BT - A Hint for Fault Healing? JF - Bulletin of the Seismological Society of America N2 - Ground‐motion prediction equations (GMPEs) are calibrated to predict the intensity of ground shaking at any given location, based on earthquake magnitude, source‐to‐site distance, local soil amplifications, and other parameters. GMPEs are generally assumed to be independent of time; however, evidence is increasing that large earthquakes modify the shallow soil conditions and those of the fault zone for months or years. These changes may affect the intensity of shaking and result in time‐dependent effects that can potentially be resolved by analyzing between‐event residuals (residuals between observed and predicted ground motion for individual earthquakes averaged over all stations). Here, we analyze a data set of about 65,000 recordings for about 1400 earthquakes in the moment magnitude range 2.5–6.5 that occurred in central Italy from 2008 to 2017 to capture the temporal variability of the ground shaking at high frequency. We first compute between‐event residuals for each earthquake in the Fourier domain with respect to a GMPE developed ad hoc for the analyzed data set. The between‐events show large changes after the occurrence of mainshocks such as the 2009 Mw 6.3 L'Aquila, the 2016 Mw 6.2 Amatrice, and Mw 6.5 Norcia earthquakes. Within the time span of a few months after the mainshocks, the between‐event contribution to the ground shaking varies by a factor 7. In particular, we find a large drop in the between‐events in the aftermath of the L'Aquila earthquake, followed by a slow positive trend that leads to a recovery interrupted by a new drop at the beginning of 2014. We also quantify the frequency‐dependent correlation between the Brune stress drop Δσ and the between‐events. We find that the temporal changes of Δσ resemble those of the between‐event residuals; in particular, during the period when the between‐events show the positive trend, the average logarithm of Δσ increases with an annual rate of 0.19 (i.e., the amplification factor for Δσ is 1.56 per year). Breakpoint analysis located a change in the linear trend coefficients of Δσ versus time in February 2014, although no large earthquakes occurred at that time. Finally, the temporal variability of Δσ mirrors the relative seismic‐velocity variations observed in previous studies for the same area and period, suggesting that both crack healing along the main fault system and healing of microcracks distributed at shallow depths throughout the surrounding region might be necessary to explain the wider observations of postearthquake recovery. Y1 - 2018 U6 - https://doi.org/10.1785/0120180078 SN - 0037-1106 SN - 1943-3573 VL - 108 IS - 4 SP - 1853 EP - 1863 PB - Seismological Society of America CY - Albany ER - TY - JOUR A1 - Cesca, Simone A1 - Braun, Thomas A1 - Maccaferri, Francesco A1 - Passarelli, Luigi A1 - Rivalta, Eleonora A1 - Dahm, Torsten T1 - Source modelling of the M5-6 Emilia-Romagna, Italy, earthquakes (2012 May 20-29) JF - Geophysical journal international N2 - On 2012 May 20 and 29, two damaging earthquakes with magnitudes M-w 6.1 and 5.9, respectively, struck the Emilia-Romagna region in the sedimentary Po Plain, Northern Italy, causing 26 fatalities, significant damage to historical buildings and substantial impact to the economy of the region. The earthquake sequence included four more aftershocks with M-w, >= 5.0, all at shallow depths (about 7-9 km), with similar WNW-ESE striking reverse mechanism. The timeline of the sequence suggests significant static stress interaction between the largest events. We perform here a detailed source inversion, first adopting a point source approximation and considering pure double couple and full moment tensor source models. We compare different extended source inversion approaches for the two largest events, and find that the rupture occurred in both cases along a subhorizontal plane, dipping towards SSW Directivity is well detected for the May 20 main shock, indicating that the rupture propagated unilaterally towards SE. Based on the focal mechanism solution, we further estimate the co-seismic static stress change induced by the May 20 event. By using the rate-and-state model and a Poissonian earthquake occurrence, we infer that the second largest event of May 29 was induced with a probability in the range 0.2-0.4. This suggests that the segment of fault was already prone to rupture. Finally, we estimate peak ground accelerations for the two main events as occurred separately or simultaneously. For the scenario involving hypothetical rupture areas of both main events, we estimate M-w = 6.3 and an increase of ground acceleration by 50 per cent. The approach we propose may help to quantify rapidly which regions are invested by a significant increase of the hazard, bearing the potential for large aftershocks or even a second main shock. KW - Earthquake dynamics KW - Earthquake source observations Y1 - 2013 U6 - https://doi.org/10.1093/gji/ggt069 SN - 0956-540X VL - 193 IS - 3 SP - 1658 EP - 1672 PB - Oxford Univ. Press CY - Oxford ER - TY - JOUR A1 - Passarelli, Luigi A1 - Rivalta, Eleonora A1 - Cesca, Simone A1 - Aoki, Yosuke T1 - Stress changes, focal mechanisms, and earthquake scaling laws for the 2000 dike at Miyakejima (Japan) JF - Journal of geophysical research : Solid earth N2 - Faulting processes in volcanic areas result from a complex interaction of pressurized fluid-filled cracks and conduits with the host rock and local and regional tectonic setting. Often, volcanic seismicity is difficult to decipher in terms of the physical processes involved, and there is a need for models relating the mechanics of volcanic sources to observations. Here we use focal mechanism data of the energetic swarm induced by the 2000 dike intrusion at Miyakejima (Izu Archipelago, Japan), to study the relation between the 3-D dike-induced stresses and the characteristics of the seismicity. We perform a clustering analysis on the focal mechanism (FM) solutions and relate them to the dike stress field and to the scaling relationships of the earthquakes. We find that the strike and rake angles of the FMs are strongly correlated and cluster on bands in a strike-rake plot. We suggest that this is consistent with optimally oriented faults according to the expected pattern of Coulomb stress changes. We calculate the frequency-size distribution of the clustered sets finding that focal mechanisms with a large strike-slip component are consistent with the Gutenberg-Richter relation with a b value of about 1. Conversely, events with large normal faulting components deviate from the Gutenberg-Richter distribution with a marked roll-off on its right-hand tail, suggesting a lack of large-magnitude events (M-w>5.5). This may result from the interplay of the limited thickness and lower rock strength of the layer of rock above the dike, where normal faulting is expected, and lower stress levels linked to the faulting style and low confining pressure. KW - dike intrusion KW - dike-induced stresses KW - dike-induced seismicity KW - Miyakejima intrusion KW - Gutenberg-Richter relationship Y1 - 2015 U6 - https://doi.org/10.1002/2014JB011504 SN - 2169-9313 SN - 2169-9356 VL - 120 IS - 6 SP - 4130 EP - 4145 PB - American Geophysical Union CY - Washington ER - TY - JOUR A1 - Passarelli, Luigi A1 - Hainzl, Sebastian A1 - Cesca, Simone A1 - Maccaferri, Francesco A1 - Mucciarelli, Marco A1 - Rößler, Dirk A1 - Corbi, Fabio A1 - Dahm, Torsten A1 - Rivalta, Eleonora T1 - Aseismic transient driving the swarm-like seismic sequence in the Pollino range, Southern Italy JF - Geophysical journal international N2 - Tectonic earthquake swarms challenge our understanding of earthquake processes since it is difficult to link observations to the underlying physical mechanisms and to assess the hazard they pose. Transient forcing is thought to initiate and drive the spatio-temporal release of energy during swarms. The nature of the transient forcing may vary across sequences and range from aseismic creeping or transient slip to diffusion of pore pressure pulses to fluid redistribution and migration within the seismogenic crust. Distinguishing between such forcing mechanisms may be critical to reduce epistemic uncertainties in the assessment of hazard due to seismic swarms, because it can provide information on the frequency-magnitude distribution of the earthquakes (often deviating from the assumed Gutenberg-Richter relation) and on the expected source parameters influencing the ground motion (for example the stress drop). Here we study the ongoing Pollino range (Southern Italy) seismic swarm, a long-lasting seismic sequence with more than five thousand events recorded and located since October 2010. The two largest shocks (magnitude M-w = 4.2 and M-w = 5.1) are among the largest earthquakes ever recorded in an area which represents a seismic gap in the Italian historical earthquake catalogue. We investigate the geometrical, mechanical and statistical characteristics of the largest earthquakes and of the entire swarm. We calculate the focal mechanisms of the M-l > 3 events in the sequence and the transfer of Coulomb stress on nearby known faults and analyse the statistics of the earthquake catalogue. We find that only 25 per cent of the earthquakes in the sequence can be explained as aftershocks, and the remaining 75 per cent may be attributed to a transient forcing. The b-values change in time throughout the sequence, with low b-values correlated with the period of highest rate of activity and with the occurrence of the largest shock. In the light of recent studies on the palaeoseismic and historical activity in the Pollino area, we identify two scenarios consistent with the observations and our analysis: This and past seismic swarms may have been 'passive' features, with small fault patches failing on largely locked faults, or may have been accompanied by an 'active', largely aseismic, release of a large portion of the accumulated tectonic strain. Those scenarios have very different implications for the seismic hazard of the area. KW - Seismicity and tectonics KW - Statistical seismology KW - Dynamics: seismotectonics Y1 - 2015 U6 - https://doi.org/10.1093/gji/ggv111 SN - 0956-540X SN - 1365-246X VL - 201 IS - 3 SP - 1553 EP - 1567 PB - Oxford Univ. Press CY - Oxford ER - TY - JOUR A1 - Mantiloni, Lorenzo A1 - Davis, Timothy A1 - Gaete Rojas, Ayleen Barbara A1 - Rivalta, Eleonora T1 - Stress inversion in a gelatin box BT - testing eruptive vent location forecasts with analog models JF - Geophysical research letters : GRL / American Geophysical Union N2 - Assessing volcanic hazard in regions of distributed volcanism is challenging because of the uncertain location of future vents. A statistical-mechanical strategy to forecast such locations was recently proposed: here, we further develop and test it with analog models. We stress a gelatin block laterally and with surface excavations, and observe air-filled crack trajectories. We use the observed surface arrivals to sample the distributions of parameters describing the stress state of the gelatin block, combining deterministic crack trajectory simulations with a Monte Carlo approach. While the individual stress parameters remain unconstrained, we effectively retrieve their ratio and successfully forecast the arrival points of subsequent cracks. KW - analog experiment KW - calderas KW - continental rifts KW - dike propagation KW - dike KW - trajectories KW - stress field Y1 - 2021 U6 - https://doi.org/10.1029/2020GL090407 SN - 0094-8276 SN - 1944-8007 VL - 48 IS - 6 PB - American Geophysical Union CY - Washington ER - TY - JOUR A1 - Namiki, Atsuko A1 - Rivalta, Eleonora A1 - Woith, Heiko A1 - Willey, Timothy A1 - Parolai, Stefano A1 - Walter, Thomas R. T1 - Volcanic activities triggered or inhibited by resonance of volcanic edifices to large earthquakes JF - Geology N2 - The existence of a causal link between large earthquakes and volcanic unrest is widely accepted. Recent observations have also revealed counterintuitive negative responses of volcanoes to large earthquakes, including decreased gas emissions and subsidence in volcanic areas. In order to explore the mechanisms that could simultaneously explain both the positive and negative responses of volcanic activity to earthquakes, we here focus on the role played by topography. In the laboratory, we shook a volcanic edifice analogue, made of gel, previously injected with a buoyant fluid. We find that shaking triggers rapid migration of the buoyant fluid upward, downward, or laterally, depending on the fluid’s buoyancy and storage depth; bubbly fluids stored at shallow depth ascend, while low-buoyancy fluids descend or migrate laterally. The migration of fluids induced by shaking is two orders of magnitude faster than without shaking. Downward or lateral fluid migration may decrease volcanic gas emissions and cause subsidence as a negative response, while upward migration is consistent both with an increase in volcanic activity and immediate unrest (deformation and seismicity) after large earthquakes. The fluid migration is more efficient when the oscillation frequency is close to the resonance frequency of the edifice. The resonance frequency for a 30-km-wide volcanic mountain range, such as those where subsidence was observed, is ∼0.07 Hz. Only large earthquakes are able to cause oscillation at such low frequencies. Y1 - 2018 U6 - https://doi.org/10.1130/G45323.1 SN - 0091-7613 SN - 1943-2682 VL - 47 IS - 1 SP - 67 EP - 70 PB - American Institute of Physics CY - Boulder ER - TY - JOUR A1 - Merz, Bruno A1 - Kuhlicke, Christian A1 - Kunz, Michael A1 - Pittore, Massimiliano A1 - Babeyko, Andrey A1 - Bresch, David N. A1 - Domeisen, Daniela I. A1 - Feser, Frauke A1 - Koszalka, Inga A1 - Kreibich, Heidi A1 - Pantillon, Florian A1 - Parolai, Stefano A1 - Pinto, Joaquim G. A1 - Punge, Heinz Jürgen A1 - Rivalta, Eleonora A1 - Schröter, Kai A1 - Strehlow, Karen A1 - Weisse, Ralf A1 - Wurpts, Andreas T1 - Impact forecasting to support emergency management of natural hazards JF - Reviews of geophysics N2 - Forecasting and early warning systems are important investments to protect lives, properties, and livelihood. While early warning systems are frequently used to predict the magnitude, location, and timing of potentially damaging events, these systems rarely provide impact estimates, such as the expected amount and distribution of physical damage, human consequences, disruption of services, or financial loss. Complementing early warning systems with impact forecasts has a twofold advantage: It would provide decision makers with richer information to take informed decisions about emergency measures and focus the attention of different disciplines on a common target. This would allow capitalizing on synergies between different disciplines and boosting the development of multihazard early warning systems. This review discusses the state of the art in impact forecasting for a wide range of natural hazards. We outline the added value of impact-based warnings compared to hazard forecasting for the emergency phase, indicate challenges and pitfalls, and synthesize the review results across hazard types most relevant for Europe. KW - impact forecasting KW - natural hazards KW - early warning Y1 - 2020 U6 - https://doi.org/10.1029/2020RG000704 SN - 8755-1209 SN - 1944-9208 VL - 58 IS - 4 PB - American Geophysical Union CY - Washington ER -