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15 pages, 10 figures, 3 tables, supplementary material https://doi.org/10.1016/j.margeo.2022.106749.-- Data availability: The data (3D complex mesh of the ARFS and rake values, and the resulting grid files of the tsunami simulations containing the maximum wave amplitude) are archived at PANGAEA repository (https://doi.pangaea.de/10.1594/PANGAEA.941092).-- The EMODnet bathymetry is available at https://www.emodnet-bathymetry.eu/. The stochastic slip distributions have been produced by the code ANTI-FASc (https://github.com/antonioscalaunina/ANTI-FASc) a platform partially based on the code k223d (Herrero and Murphy, 2018 available at https://github.com/s-murfy/k223d), in turn based on the slipk2 (available at https://github.com/andherit/slipk2) and the trilateration codes (available at https://github.com/andherit/trilateration), The westernmost Mediterranean hosts part of the plate boundary between the European and African tectonic plates. Based on the scattered instrumental seismicity, this boundary has been traditionally interpreted as a wide zone of diffuse deformation. However, recent seismic images and seafloor mapping studies support that most of the plate convergence may be accommodated in a few tectonic structures, rather than in a broad region. Historical earthquakes with magnitudes Mw > 6 and historical tsunamis support that the low-to-moderate instrumental seismicity might also have led to underestimation of the seismogenic and tsunamigenic potential of the area. We evaluate the largest active faults of the westernmost Mediterranean: the reverse Alboran Ridge, and the strike-slip Carboneras, Yusuf and Al-Idrissi fault systems. For the first time, we use a dense grid of modern seismic data to characterize the entire dimensions of the main fault systems, accurately describe the geometry of these structures and estimate their seismic source parameters. Tsunami scenarios have been tested based on 3D-surfaces and seismic source parameters, using both uniform and heterogeneous slip distributions. The comparison of our results with previous studies, based on limited information on the fault geometry and kinematics, indicates that accurate fault geometries and heterogeneous slip distributions are needed to properly assess the seismic and tsunamigenic potential in this area. Based on fault scaling relations, the four fault systems have a large seismogenic potential, being able to generate earthquakes with Mw > 7. The reverse Alboran Ridge Fault System has the largest tsunamigenic potential, being able to generate a tsunami wave amplitude greater than 3 m in front of the coasts of Southern Spain and Northern Africa, This work is supported by the Cluster of Excellence “The Future Ocean”, within the framework of the Excellence Initiative by the Deutsche Forschungsgemeinschaft (DFG) on behalf of the German federal and state governments. This study benefited from an EU Marie Skłodowska-Curie Individual Fellowship to LGP (H2020-MSCA-IF-2017 796013). LGP, CS, FM and RB acknowledge the resources made available by the SISMOLAB-3D at INGV. This work has been carried out in collaboration with the Grup de Recerca Consolidat de la Generalitat de Catalunya “Barcelona Center for Subsurface Imaging” (2017 SGR 1662), and acknowledges the ICM “Severo Ochoa Centre of Excellence” accreditation (CEX2019-000928-S)

SUMMARYWe investigated the kinematic rupture model of the 2018 Mw 6.8 Zakynthos, Ionian Sea (Greece), earthquake by using a non-linear joint inversion of strong motion data, high-rate GPS time-series and static coseismic GPS displacements. We also tested inversion results against tide-gauge recordings of the small tsunami generated in the Ionian Sea. In order to constrain the fault geometry, we performed several preliminary kinematic inversions by assuming the parameter values resulting from different published moment tensor solutions. The lowest cost function values were obtained by using the geometry derived from the United States Geological Survey (USGS) focal solution. Between the two conjugate USGS planes, the rupture model which better fits the data is the one with the N9°E-striking 39°ESE-dipping plane. The rupture history of this model is characterized by a bilateral propagation, featuring two asperities; a main slip patch extending between 14 and 28 km in depth, 9 km northeast from the nucleation and a slightly shallower small patch located 27 km southwest from the nucleation. The maximum energy release occurs between 8 and 12 s, when both patches are breaking simultaneously. The maximum slip is 1.8 m and the total seismic moment is 2.4 × 1019 Nm, corresponding to a Mw value of 6.8. The slip angle shows a dominant right-lateral strike-slip mechanism, with a minor reverse component that increases on the deeper region of the fault. This result, in addition to the observed possibility of similar mechanisms for previous earthquakes occurred in 1959 and 1997, suggests that the tectonic deformation between the Cephalonia Transform Fault Zone and the northern tip of the Hellenic Arc Subduction zone may be accommodated by prevailing right lateral low-dipping faults, occurring on re-activated structures previously experiencing (until Pliocene) compressional regime. Comparison of predicted and observed tsunami data suggests the need of a better characterization of local harbour response for this type of relatively short-wavelength events, which is important in the context of tsunami early warning. However, the suggested dominantly strike-slip character would in turn imply a reduced tsunami hazard as compared to a dominant thrust faulting regime from this source region.

The Italian Tsunami Alert Center based at the Istituto Nazionale di Geofisica e Vulcanologia (CAT-INGV) has been monitoring the Mediterranean seismicity in the past 8 yr to get fast and reliable information for seismically induced tsunami warnings. CAT-INGV is a tsunami service provider in charge of monitoring the seismicity of the Mediterranean Sea and of alerting Intergovernmental Oceanographic Commission (IOC)/UNESCO subscriber Member States and the Italian Department of Civil Protection of a potentially impending tsunami, in the framework of the Tsunami Warning and Mitigation System in the North-eastern Atlantic, the Mediterranean and connected seas (NEAMTWS). CAT-INGV started operating in 2013 and became operational in October 2016. Here, after describing the NEAMTWS in the framework of the global effort coordinated by IOC/UNESCO, we focus on the tsunami hazard in the Mediterranean Sea. We then describe CAT-INGV mandate, functioning, and operational procedures. Furthermore, the article discusses the lessons learned from past events occurring in the Mediterranean Sea, such as the Kos-Bodrum in 2017 (Mw 6.6) and the Samos-Izmir in 2020 (Mw 7.0) earthquakes, which generated moderately damaging tsunamis. Based on these lessons, we discuss some potential improvements for the CAT-INGV and the NEAMTWS, including better seismic and sea level instrumental coverage. We emphasize the need for tsunami risk awareness raising, better preparation, and full implementation of the tsunami warning “last-mile” to foster the creation of a more integrated, interoperable, and sustainable risk reduction framework. If we aim to be better prepared for the next tsunami, these important challenges should be prioritized in the agenda of the IOC/UNESCO Member States and the European Commission.

The tsunami source of the 2021 MW 8.1 Raoul Island earthquake in the Kermadec subduction zone was estimated by inverting the tsunami signals recorded by Deep-ocean Assessment and Reporting of Tsunamis (DART) bottom pressure sensors and coastal tide-gauges. The main asperity of up to 5 m of slip is located northeastward from the hypocenter, with features compatible with the aftershock distribution and rapid back-projection analysis. Three earthquakes of MW ∼8 or larger which also produced moderate tsunamis happened in the 20th century in the same portion of the subduction zone. This is the first great tsunamigenic event captured by the new New Zealand DART network in the South West Pacific, which proved valuable to estimate a robust image of the tsunami source. We also show a first proof of concept of the capability of this network to reduce the uncertainty associated with tsunami forecasting and to increase the lead time available for evacuation for future alerts.

We present a source solution for the tsunami generated by the Mw 6.6 earthquake that occurred on May 2, 2020, about 807thinsp;km offshore south of Crete, in the Cretan Passage, on the shallow portion of the Hellenic Arc Subduction Zone (HASZ). The tide-gauges recorded this local tsunami on the southern coast of Crete island and Kasos island. We used these tsunami observations to constrain the geometry and orientation of the causative fault, the rupture mechanism and the slip amount. We first modelled an ensemble of synthetic tsunami waveforms at the tide-gauge locations, produced for a range of earthquake parameter values as constrained by some of the available moment tensor solutions. We allow for both a splay and a back-thrust fault, corresponding to the two nodal planes of the moment tensor solution. We then measured the misfit between the synthetic and the observed marigrams for each source parameter set. Our results identify the shallow steeply-dipping back-thrust fault as the one producing the lowest misfit to the tsunami data. However, a rupture on a lower angle fault, possibly a splay fault, with a sinistral component due to the oblique convergence on this segment of the HASZ, cannot be completely ruled out. This earthquake reminds us that the uncertainty regarding potential earthquake mechanisms at a specific location remains quite significant. In this case, for example, it is not possible to anticipate if the next event will be one occurring on the subduction interface, on a splay fault, or on a back-thrust which seems the most likely for the event under investigation. This circumstance bears important consequences because back-thrust and splay faults might enhance the tsunamigenic potential with respect to the subduction interface due to their steeper dip. Then, these results are relevant for tsunami forecasting both in the framework of the long-term hazard assessment and of the early warning systems.

Seismological, tsunami and geodetic observations have shown that subduction zones are complex systems where the properties of earthquake rupture vary with depth as a result of different pre-stress and frictional conditions. A wealth of earthquakes of different sizes and different source features (e.g. rupture duration) can be generated in subduction zones, including tsunami earthquakes, some of which can produce extreme tsunamigenic events. Here, we offer a geological perspective principally accounting for depth-dependent frictional conditions, while adopting a simplified distribution of on-fault tectonic pre-stress. We combine a lithology-controlled, depth-dependent experimental friction law with 2D elastodynamic rupture simulations for a Tohoku-like subduction zone cross-section. Subduction zone fault rocks are dominantly incohesive and clay-rich near the surface, transitioning to cohesive and more crystalline at depth. By randomly shifting along fault dip the location of the high shear stress regions (“asperities”), moderate to great thrust earthquakes and tsunami earthquakes are produced that are quite consistent with seismological, geodetic, and tsunami observations. As an effect of depth-dependent friction in our model, slip is confined to the high stress asperity at depth; near the surface rupture is impeded by the rock-clay transition constraining slip to the clay-rich layer. However, when the high stress asperity is located in the clay-to-crystalline rock transition, great thrust earthquakes can be generated similar to the Mw 9 Tohoku (2011) earthquake.

The 2015/11/17 Lefkada (Greece) earthquake ruptured a segment of the Cephalonia Transform Fault (CTF) where probably the penultimate major event was in 1948. Using near-source strong motion and high sampling rate GPS data and Sentinel-1A SAR images on two tracks, we performed the inversion for the geometry, slip distribution and rupture history of the causative fault with a three-step self-consistent procedure, in which every step provided input parameters for the next one. Our preferred model results in a ~70° ESE-dipping and ~13° N-striking fault plane, with a strike-slip mechanism (rake ~169°) in agreement with the CTF tectonic regime. This model shows a bilateral propagation spanning ~9 s with the activation of three main slip patches, characterized by rise time and peak slip velocity in the ranges 2.5–3.5 s and 1.4–2.4 m/s, respectively, corresponding to 1.2–1.8 m of slip which is mainly concentrated in the shallower (0 = 1.05 × 1019 N m) suggest a magnitude of M w 6.6. Our best solution suggests that the occurrence of large (M w > 6) earthquakes to the northern and to the southern boundaries of the 2015 causative fault cannot be excluded.

We propose a procedure for uncertainty quantification in Probabilistic Tsunami Hazard Analysis (PTHA), with a special emphasis on the uncertainty related to statistical modelling of the earthquake source in Seismic PTHA (SPTHA), and on the separate treatment of subduction and crustal earthquakes (treated as background seismicity). An event tree approach and ensemble modelling are used in spite of more classical approaches, such as the hazard integral and the logic tree. This procedure consists of four steps: (1) exploration of aleatory uncertainty through an event tree, with alternative implementations for exploring epistemic uncertainty; (2) numerical computation of tsunami generation and propagation up to a given offshore isobath; (3) (optional) site-specific quantification of inundation; (4) simultaneous quantification of aleatory and epistemic uncertainty through ensemble modelling. The proposed procedure is general and independent of the kind of tsunami source considered; however, we implement step 1, the event tree, specifically for SPTHA, focusing on seismic source uncertainty. To exemplify the procedure, we develop a case study considering seismic sources in the Ionian Sea (central-eastern Mediterranean Sea), using the coasts of Southern Italy as a target zone. The results show that an efficient and complete quantification of all the uncertainties is feasible even when treating a large number of potential sources and a large set of alternative model formulations. We also find that (i) treating separately subduction and background (crustal) earthquakes allows for optimal use of available information and for avoiding significant biases; (ii) both subduction interface and crustal faults contribute to the SPTHA, with different proportions that depend on source-target position and tsunami intensity; (iii) the proposed framework allows sensitivity and deaggregation analyses, demonstrating the applicability of the method for operational assessments.

Tsunami waveform inversion is often used to retrieve information about the causative seismic tsunami source. Tide-gauges record tsunamis routinely; however, compared to deep-ocean sensor data, tide-gauge waveform modeling is more difficult due to coarse/inaccurate local bathymetric models resulting in a time mismatch between observed and predicted waveforms. This can affect the retrieved tsunami source model, thus limiting the use of tide-gauges data. A method for nonlinear inversion with an automatic optimal time-alignment (OTA), calculated by including a time shift parameter in the cost function, is presented. The effectiveness of the method is demonstrated through a series of synthetic tests and is applied as part of a joint inversion with InSAR data for the slip distribution of the 2015 Mw8.3 Illapel earthquake. The results show that without OTA the resolution on the slip model degrades significantly and that using this method for a real case strongly affects the retrieved slip pattern.

SUMMARY In this study, we investigate the rupture history of the 2009 April 6 (Mw 6.1) L’Aquila normal faulting earthquake by using a non-linear inversion of strong motion, GPS and DInSAR data. Both the separate and joint inversion solutions reveal a complex rupture process and a heterogeneous slip distribution. Slip is concentrated in two main asperities: a smaller shallow patch of slip located updip from the hypocentre and a second deeper and larger asperity located southeastwards along-strike direction. The key feature of the source process emerging from our inverted models concerns the rupture history, which is characterized by two distinct stages. The first stage begins with rupture nucleation and with updip propagation at relatively high (∼4.0 km s−1), but still subshear, rupture velocity. The second stage starts nearly 2.0–2.5 s after nucleation and it is characterized by the along-strike rupture propagation. The largest and deeper asperity fails during this stage of the rupture process. The rupture velocity is larger in the updip than in the along-strike direction. The updip and along-strike rupture propagation are separated in time and associated with a Mode II and a Mode III crack, respectively. The comparison between the source models inferred in this study with the Poisson ratio anomalies in the crustal volume containing the fault plane allows the interpretation of the delay in along-strike rupture propagation in terms of a structural control of the rupture history. Our results show that the L’Aquila earthquake featured a very complex rupture, with strong spatial and temporal heterogeneities suggesting a strong frictional and/or structural control of the rupture process.

The Mw 8.8 Chile earthquake on 27 February 2010 occurred in a broad region where tectonic loading has been accumulating since the great 1835 earthquake. A joint inversion of tsunami and geodetic data suggests that the 2010 earthquake rupture only partly overlapped with the zone of preseismic locking.

On 6 April 2009, a magnitude Mw = 6.1 earthquake struck the Abruzzi region in central Italy. Despite its moderate size, the earthquake caused more than 300 fatalities and partially destroyed the city of L'Aquila and many surrounding villages. The mainshock was preceded by an earthquake swarm that started at the end of 2008. The largest earthquakes of the swarm included an Mw = 4.0, which occurred on 2009/03/30 at 13:38:26 (UTC), and Mw = 3.9 and Mw = 3.5 events that occurred on 2009/04/05 at 20:48 and 22:39 (UTC), respectively. By the end of November 2009, more than 16,000 aftershocks with ML ≥ 0.5 had been recorded by the INGV seismic network (Figure 1). Current advances in data transmission and communication yield high-quality broadband velocity and strong-motion waveforms in near real time. These data are all crucial for rapid determination of earthquake source parameters ( e.g. , fault geometry, focal depth, and seismic moment). For the L'Aquila mainshock, the velocimeter data of the Italian National Seismic Network (INSN, code IV), MedNet (code MN, station PDG), the North-East Italy Broadband Network (code NI, stations ACOM and PALA), and the SudTirol Province (code SI, station KOSI) were available in real time. In the following days, the strong-motion data of the RAN network (Rete Accelerometrica Nazionale) and, in addition, the displacement data recorded by the Istituto Nazionale di Geofisica e Vulcanologia (INGV) GPS network (Anzidei et al. 2009) also become available. In this study we present a retrospective analysis of the rapid source parameters determination procedure developed at INGV (Scognamiglio et al. 2009) as applied to the L'Aquila seismic sequence. Our approach consists of two stages: the near real-time determination of the seismic moment tensor, which is already routinely performed for all ML ≥ 3.5 earthquakes …

SUMMARY In this study, we aim to understand the dependence of the critical slip weakening distance (D c) on the final slip (D tot) during the propagation of a dynamic rupture and the consistency of their inferred correlation. To achieve this goal we have performed a series of numerical tests suitably designed to validate the adopted numerical procedure and to verify the actual capability in measuring D c. We have retrieved two kinematic rupture histories from spontaneous dynamic rupture models governed by a slip weakening law in which a constant D c distribution on the fault plane as well as a constant D c/D tot ratio are assumed, respectively. The slip velocity and the shear traction time histories represent the synthetic ‘real’ target data which we aim to reproduce. We use a 3-D traction-at-split nodes numerical procedure to image the dynamic traction evolution by assuming our modelled slip velocity as a boundary condition on the fault plane. We assume a regularized Yoffe function as source time function in our modelling attempts and we measure the critical slip weakening distance from the inferred traction versus slip curves at each point on the fault. We compare the inferred values with those of the target dynamic models. Our numerical tests show that fitting the slip velocity functions of the target models at each point on the fault plane is not enough to retrieve good traction evolution curves and to obtain reliable measures of D c. We find that the estimation of D c is very sensitive to any small variation of the slip velocity function. An artificial correlation between D c/D tot is obtained when a fixed shape of slip velocity is assumed on the fault (i.e. constant rise time and constant time for positive acceleration) which differs from that of the target model. We point out that the estimation of fracture energy (breakdown work) on the fault is not affected by biases in measuring D c.

We calculated the expected impact on the Italian coast of the Adriatic Sea of a large set of tsunamis resulting from potential earthquakes generated by major fault zones. Our approach merges updated knowledge on the regional tectonics and scenario-like calculations of expected tsunami impact. We selected six elongated potential source zones. For each of them we determined a Maximum Credible Earthquake and the associated Typical Fault, described by its size, geometry and kinematics. We then let the Typical Fault float along strike of its parent source zone and simulated all tsunamis it could generate. Simulations are based on the solution of the nonlinear shallow water equations through a finite-difference technique. For each run we calculated the wavefields at specified simulation times and the maximum water height field (above mean sea level), then generated travel-time maps and maximum water height profiles along the target coastline. Maxima were also classified in a three-level code of expected tsunami threat. We found that the southern portion of Apulia facing Albania and the Gargano promontory are especially prone to the tsunami threat. We also found that some bathymetric features are crucial in determining the focalization-defocalization of tsunami energy. We suggest that our results be taken into account in the design of early-warning strategies.

The 18 April 1906 M ∼8 California earthquake generated a small local tsunami that was recorded in the near field by the Presidio, San Francisco tide gauge located near the Golden Gate. We investigate the causative, tsunamigenic, seismic source by forward modeling and nonlinear inversion of the Presidio marigram. We use existing seismological and geological observations to fix the fault system geometry and the surface slip on the onland portions of the San Andreas fault (SAF). We perform synthetic inversions to show that the single, near-field marigram constrains the main features of the rupture on the portion of the SAF system offshore of the Golden Gate. Finally, we perform nonlinear inversions for the slip distribution and the timing of the rupture of the 1906 earthquake. Our results, in agreement with previous studies, identify a dilatational stepover and show a bilateral rupture, possibly originating or propagated through the stepover region. We find that little or no coseismic slip on normal faults in the stepover region is required to fit the marigram, and we obtain adequate fits when allowing delays in the source initiation times of up to 3 min on the various fault segments. We constrain slip to be of about 5–6 m for the onshore portion of the SAF to the northwest of the Golden Gate, in agreement with 1906 surface observations of fault offset. Our results favor the hypothesis of a vertical dip for a currently aseismic SAF to the southeast of the Golden Gate, under the San Francisco peninsula.

Several independent indicators imply a high probability of a great ( M > 8) earthquake rupture of the subduction megathrust under the Mentawai Islands of West Sumatra. The human consequences of such an event depend crucially on its tsunamigenic potential, which in turn depends on unpredictable details of slip distribution on the megathrust and how resulting seafloor movements and the propagating tsunami waves interact with bathymetry. Here we address the forward problem by modelling about 1000 possible complex earthquake ruptures and calculating the seafloor displacements and tsunami wave height distributions that would result from the most likely 100 or so, as judged by reference to paleogeodetic data. Additionally we carry out a systematic study of the importance of the location of maximum slip with respect to the morphology of the fore-arc complex. Our results indicate a generally smaller regional tsunami hazard than was realised in Aceh during the December 2004 event, though more than 20% of simulations result in tsunami wave heights of more than 5 m for the southern Sumatran cities of Padang and Bengkulu. The extreme events in these simulations produce results which are consistent with recent deterministic studies. The study confirms the sensitivity of predicted wave heights to the distribution of slip even for events with similar moment and reproduces Plafker's rule of thumb. Additionally we show that the maximum wave height observed at a single location scales with the magnitude though data for all magnitudes exhibit extreme variability. Finally, we show that for any coastal location in the near field of the earthquake, despite the complexity of the earthquake rupture simulations and the large range of magnitudes modelled, the timing of inundation is constant to first order and the maximum height of the modelled waves is directly proportional to the vertical coseismic displacement experienced at that point. These results may assist in developing tsunami preparedness strategies around the Indian Ocean and in particular along the coasts of western Sumatra.

SUMMARY We introduce a rapid and robust, energy-duration procedure, based on the Haskell, extended-source model, to obtain an earthquake moment and a moment magnitude, MED. Using seismograms at teleseismic distances (30°–90°), this procedure combines radiated seismic energy measures on the P to S interval of broadband signals and source duration measures on high-frequency, P-wave signals. The MED energy-duration magnitude is scaled to correspond to the Global Centroid-Moment Tensor (CMT) moment-magnitude, MCMTw, and can be calculated within about 20 min or less after origin time (OT). The measured energy and duration values also provide the energy-to-moment ratio, Θ, used for identification of tsunami earthquakes. The MED magnitudes for a set of recent, large earthquakes match closely MCMTw, even for the largest, great earthquakes; these results imply that the MED measure is accurate and does not saturate. After the 2004 December 26 Sumatra-Andaman mega-thrust earthquake, magnitude estimates available within 1 hr of OT ranged from M= 8.0 to 8.5, the CMT magnitude, available about 3 hr after OT, was MCMTw= 9.0, and, several months after the event, Mw= 9.1–9.3 was obtained from analysis of the earth normal modes. The energy-duration magnitude for this event is MED= 9.2, a measure that is potentially available within 20 min after OT. After the 2006 July 17, Java earthquake, the magnitude was evaluated at M= 7.2 at 17 min after OT, the CMT magnitude, available about 1 hr after OT, was MCMTw= 7.7; the energy-duration results for this event give MED= 7.8, with a very long source duration of about 160 s, and a very low Θ value, indicating a possible tsunami earthquake.

The aim of this work is to infer the slip distribution and rupture velocity along the rupture zone of the 26 December 2004 Sumatra–Andaman earthquake from available tide gage records of the tsunami. We selected waveforms from 14 stations, distributed along the coast of the Indian Ocean. Then we subdivided the fault plane into 16 subfaults (both along strike and downdip) following the geometry and mechanism proposed by Banerjee et al. (2005) and computed the corresponding Green’s functions by numerical solution of the shallow-water equations through a finite- difference method. The slip distribution and rupture velocity were determined simultaneously by means of a simulated annealing technique. We compared the recorded and synthetic waveforms in the time domain, using a cost function that is a trade-off between the L1 and L2 norms. Preliminary tests on a synthetic dataset, together with a posteriori statistical analysis of the model ensemble enabled us to assess the effectiveness of the method and to quantify the model uncertainty. The main finding is that the best source model features a nonuniform distribution of coseismic slip, with high slip values concentrated into three main patches: the first is located in the southern part of the fault, off the coast of the Aceh Province; the second between 6.5° N and 11° N; and the third at depth, between 11° N and 14° N. Furthermore, we estimated that the rupture propagated at an average speed of 2.0 km/sec.

In this paper we present and discuss the performance of the procedure for earthquake location and characterization implemented in the Italian Candidate Tsunami Service Provider at the Istituto Nazionale di Geofisica e Vulcanologia (INGV) in Rome. Following the ICG/NEAMTWS guidelines, the first tsunami warning messages are based only on seismic information, i.e., epicenter location, hypocenter depth, and magnitude, which are automatically computed by the software Early-est. Early-est is a package for rapid location and seismic/tsunamigenic characterization of earthquakes. The Early-est software package operates using offline-event or continuous-real-time seismic waveform data to perform trace processing and picking, and, at a regular report interval, phase association, event detection, hypocenter location, and event characterization. Early-est also provides mb, Mwp, and Mwpd magnitude estimations. mb magnitudes are preferred for events with Mwp ≲ 5.8, while Mwpd estimations are valid for events with Mwp ≳ 7.2. In this paper we present the earthquake parameters computed by Early-est between the beginning of March 2012 and the end of December 2014 on a global scale for events with magnitude M ≥ 5.5, and we also present the detection timeline. We compare the earthquake parameters automatically computed by Early-est with the same parameters listed in reference catalogs. Such reference catalogs are manually revised/verified by scientists. The goal of this work is to test the accuracy and reliability of the fully automatic locations provided by Early-est. In our analysis, the epicenter location, hypocenter depth and magnitude parameters do not differ significantly from the values in the reference catalogs. Both mb and Mwp magnitudes show differences to the reference catalogs. We thus derived correction functions in order to minimize the differences and correct biases between our values and the ones from the reference catalogs. Correction of the Mwp distance dependency is particularly relevant, since this magnitude refers to the larger and probably tsunamigenic earthquakes. Mwp values at stations with epicentral distance Δ ≲ 30° are significantly overestimated with respect to the CMT-global solutions, whereas Mwp values at stations with epicentral distance Δ ≳ 90° are slightly underestimated. After applying such distance correction the Mwp provided by Early-est differs from CMT-global catalog values of about δ Mwp ≈ 0.0 ∓ 0.2. Early-est continuously acquires time-series data and updates the earthquake source parameters. Our analysis shows that the epicenter coordinates and the magnitude values converge within less than 10 min (5 min in the Mediterranean region) toward the stable values. Our analysis shows that we can compute Mwp magnitudes that do not display short epicentral distance dependency overestimation, and we can provide robust and reliable earthquake source parameters to compile tsunami warning messages within less than 15 min after the event origin time.

This is a rather unusual comment that focuses on how a specific figure was constructed rather than on actual scientific results. The figure in question (Figure 9 from Pino et al. 2009) does not even show new data or results, but is simply a summary of slip models that have been proposed in the literature for the 1908 earthquake. All models describe slip distributions from coseismic elevation changes except for one, derived by Pino et al. (2000) based on waveform modeling of historical seismograms. To construct Figure 9 we simply plotted the slip maxima obtained by different workers in a 2D diagram having the northward distance from a conventional point in the Ionian Sea on the x -axis and slip on the y -axis. The first two sentences of its caption read: “Slip distribution along-strike of the fault resulting from various studies. The diagram consistently shows the maximum slip recorded along each section of the fault.” The distribution reported as “Amoruso et al. (2002)” was based on their Model A (see our Figure 1 and Figure 1B of the comment). Model A exhibits two prominent maxima (respectively a and c in our Figure 1), described as follows in Amoruso et al. (2002): “the majority of the seismic moment is released in a region, ∼ 600 km2 in area, extending south of the Calabrian coastline (the highest slip is ∼ 6 m at a depth of ∼ 6 km); a smaller slip patch is 25 km NE of the Ganzirri peninsula, at a depth of ∼ 17 km.” Amoruso et al. (2010) claim that Figure 9 is “inconsistent and misleading”; they never explicitly say why, but propose an alternative, more subjective way of plotting the same data. We firmly believe our Figure 9 was constructed in a plain and easily …

Summary This paper presents a study of the tsunami following the disastrous earthquake that occurred on the 8th of September 1905 in Calabria, southern Italy. The shock caused devastation in many towns and villages leading to more than 500 victims. According to coeval sources the tsunami was not catastrophic, but was large enough to inundate low lying lands in several coastal segments and to affect boats. No specific study was ever devoted to this tsunami in the literature. Our analysis is carried out by means of numerical modelling and aims at filling this gap. Since the source fault of the earthquake has not yet been identified, we study three tsunamis produced by likely potential sources, according to macroseismic data and the seismotectonic knowledge of the region, namely the Capo Vaticano (CV) fault, the Vibo Valentia (VV) fault and the Lamezia (LA) fault. We compute tsunami waves under the hypotheses that the sea floor deformation is caused by a shear double-couple dislocation taking place over a rectangular fault and that sea waves propagate according to the shallow water approximation. The three tsunamis cause either a pure initial depression (VV and LA) or a predominant initial depression (CV) of the sea surface in the gulf of St. Eufemia. One very relevant finding is that tsunami energy is trapped within a narrow channel along the Calabrian coast to the north of the source with the consequence that wave amplitudes computed here are much larger than the values expected in the case of an ordinary energy decay law with distance; energy trapping along southern coastal segments is less efficient. Only a small fraction of tsunami energy penetrates the Straits of Messina to the south. Propagation to the west is affected by the Aeolian islands that produce a quasi-shadow zone on the side opposite to the tsunami impact. The LA tsunami is found to be too weak to be compatible with observations. A sensitivity analysis concerning some parameters of the faults (namely length, width and slip magnitude) has been performed in order to explore their influence on the tsunami features. The main result of this paper is that we cannot discriminate between the CV and VV sources: both are in agreement with some historical observations, whilst they do not match others. We believe that a better tuning of the source mechanism over these faults can improve the agreement between model computations and historical observations.

[1] We image the rupture history of the 2009 L'Aquila (central Italy) earthquake using a nonlinear joint inversion of strong motion and GPS data. This earthquake ruptured a normal fault striking along the Apennines axis and dipping to the SW. The inferred slip distribution is heterogeneous and characterized by a small, shallow slip patch located up-dip from the hypocenter (9.5 km depth) and a large, deeper patch located southeastward. The rupture velocity is larger in the up-dip than in the along-strike direction. This difference can be partially accounted by the crustal structure, which is characterized by a high velocity layer above the hypocenter and a lower velocity below. The latter velocity seems to have affected the along strike propagation since the largest slip patch is located at depths between 9 and 14 km. The imaged slip distribution correlates well with the on-fault aftershock pattern as well as with mapped surface breakages.

The 2011 Tohoku earthquake (Mw = 9.1) highlighted previously unobserved features for megathrust events, such as the large slip in a relatively limited area and the shallow rupture propagation. We use a Finite Element Model (FEM), taking into account the 3D geometrical and structural complexities up to the trench zone, and perform a joint inversion of tsunami and geodetic data to retrieve the earthquake slip distribution. We obtain a close spatial correlation between the main deep slip patch and the local seismic velocity anomalies, and large shallow slip extending also to the North coherently with a seismically observed low-frequency radiation. These observations suggest that the friction controlled the rupture, initially confining the deeper rupture and then driving its propagation up to the trench, where it spreads laterally. These findings are relevant to earthquake and tsunami hazard assessment because they may help to detect regions likely prone to rupture along the megathrust, and to constrain the probability of high slip near the trench. Our estimate of ~40 m slip value around the JFAST (Japan Trench Fast Drilling Project) drilling zone contributes to constrain the dynamic shear stress and friction coefficient of the fault obtained by temperature measurements to ~0.68 MPa and ~0.10, respectively.

The islands in the Marquesas archipelago are most exposed to far-field tsunamis in French Polynesia. Four recent earthquakes located at the Pacific rim (Kurile 1994, Chile 1995, Mexico 1995 and Peru 1996 earthquakes) generated trans-Pacific tsunamis and caused contrasting inundations in several inhabited Marquesian bays. The aim of this study is to better understand the amplification phenomena observed in the Marquesas Islands and to improve the risk assessment. We present here numerical simulations of these four tsunamis by means of a finite difference model solving the equations of tsunami propagation at different scales. The water heights computed in the bays are in excellent agreement with the available observations and thus validate our numerical method. These numerical results allow us to determine (1) which propagation azimuths are dangerous for the whole Marquesas archipelago and (2) the behavior of each studied bay (amplitude, frequency) in response to tsunami waves. We observe that the seismogenic subduction zone along South America is likely to define one of the most dangerous tsunami generation areas for the Marquesas archipelago, owing to the source geometries and to the trapping of the tsunami energy by bathymetric features in the southern Pacific Ocean (fracture zones, seamount chains).

Summary Deep and large submarine slumps may generate tsunamis as disastrous as tsunamis of tectonic origin. Such a landslide is likely to be the origin of the 1998 July 17 tsunami of Papua New Guinea, the deadliest tsunami in the last 50 years. Water waves devastated a 20 km stretch of coastline, wiping out three villages and killing more than 2200 people. A numerical model has been developed to study the efficiency of deep slumps in producing tsunamis and has been applied to the Papua New Guinea event. The landslide is treated as the flow of a homogeneous gravity-driven continuum governed by a rheological law. Water waves are generated by sea-bottom displacements induced by the landslide. The shallow-water approximation is adopted for both the landslide and the associated water waves. The resulting differential equations are solved by a finite difference method based on shock-capturing. The shallow-water hypothesis is tested by comparison with a model solving Navier–Stokes equations for a mixture of water and sediments. Sensitivity tests carried out for a 2-D simplified geometry show that the water surface profile depends strongly on the constitutive law of the landslide. The 1998 event is simulated numerically by the shallow-water model, testing different friction laws. The observed inundation height distribution is well reproduced by the model for a volume of 4 km3, with its top located at a water depth of 550 m, and sliding with a Coulomb-type friction law over a distance of 5 km.

[1] We infer the slip distribution and average rupture velocity of the magnitude MW 8.4 September 12, 2007, southern Sumatra earthquake from available tide-gauge records of the ensuing tsunami. We select 9 waveforms recorded along the west coast of Sumatra and in the Indian Ocean. Slip distribution and rupture velocity are determined simultaneously by means of a non linear inversion method. We find high slip values (∼10 m) into a patch 100 km long and 50 km large, between 20 and 30 km of depth, about 100 km north-west from the epicenter. We conclude this earthquake did not rupture the whole area of the 1833 event, indicating some slip has still to occur. Our estimate of rupture velocity is of 2.1 ± 0.4 km/sec. The relatively large depth of the main slip patch is the likely explanation for the low damaging observed tsunami.

Modest earthquakes may trigger large submarine landslides, responsible for disastrous tsunami waves, as demonstrated by the Papua New Guinea event of July 17, 1998. The relatively small earthquake was followed by unexpectedly high waves, up to 15 m, wiping out 3 villages and killing more than 2200 people. Numerical simulations show that seismic dislocation sources are not energetic enough to reproduce the observed tsunami along the coast. Tsunami generation by a submarine landslide has been simulated by a finite-difference model, assimilating the landslide to a flow of granular material. Long-wave approximation is adopted for both water waves and the slide. Numerical results show that observed inundation heights are well reproduced for a volume of 4 km³ located 20 km offshore, sliding downslope with a Coulomb-type friction.

On October 4, 1994, an earthquake of magnitude M w = 8.2 occurred in the western part of the Kurile Islands, generating a tsunami that has been well recorded along the entire coast of Japan Previous works have shown that this earthquake does not represent a low angle thrust event, normally expected in a subduction zone, rather an intra-plate event rupturing through the slab. On the basis of the accepted mechanism, two fault models, representative of the nodal plane ambiguity, have been suggested. The goal of this work is to verify whether the tsunami simulations are able to rule out one of the two proposed fault models. Taking into account both fault models together with a heterogeneous slip along the fault, we have performed numerical simulations of the tsunami. All source models produce tide-gauge records in agreement with the observed ones. The limit of resolution of the performed simulations, estimated by means of a perturbed bathymetry, does not allow us to distinguish the best source model.

We present what is to our knowledge the first direct observation of the deformation of the surface of the ocean upon passage of a tsunami wave, on the high seas, far from the influence of shorelines and continental shelves. We use satellite altimetry data from the ERS-1 and TOPEX/POSEIDON programs, complemented by spectrogram techniques and synthetic maregrams to examine the case of seven recent tsunamigenic earthquakes. We make a positive identification of the tsunami wave field in the case of the 1992 Nicaraguan tsunami, which we detect at 15°S, 106°W, five hours after origin time. We model the observed spectrogram by injecting a synthetic of variable amplitude into the signal of a repetitive cycle of the satellite along the same track, concluding that the Nicaraguan tsunami had a zero-to-peak amplitude of 8 cm in that region. In the case of the 1995 Chilean tsunami, a large scatter in the spectral properties of the reference tracks renders the detection tentative. We fail to detect the tsunamis of five other large events, including the 1996 Biak and 1996 Peru earthquakes, primarily on account of unfavorable source directivity in the geometry of existing satellite tracks, and of the strong and incoherent noise produced by large current systems, such as the Kuroshio in the Northwest Pacific.

The 1908 Messina Straits tsunami is the last catastrophic event that hit the Italian coast. The parent earthquake may be considered one of the strongest shocks reported in Italian seismic catalogues. Several source models have been; proposed in the literature that are quite different with regard to almost all the fault parameters. The aim of this work is to evaluate whether tsunami data can add reliable inforiration for the identification of the fault mechanism of this earthquake. Tsunamis generated by two of the faults proposed in the literature were simulated via finite-element modelling in a former work (see Piatanesi et al., 1998): the results were in good agreement with the observations as regards the polarity of the first wave, whereas a relevant disagreement was found as far as run-up data were concerned. In this paper, that may be considered the continuation of the previous work, we focus on a particular fault, the one proposed by Capuano et al. (1988), and simulate the consequent tsunami adding two new features to possibly improve the agreement with run-up observations: i) an algorithm allowing for the effect of the sea bottom bathymetry on the tsunami initial condition, and ii) a heterogeneous slip distribution on the fault.

The earthquake we are dealing with occurred on December 28, 1908: because of the number of victims (about 60,000) and the extension of the destroyed area (6,000 km 2 ), this earthquake with the epicentral MCS intensity XI may be considered the strongest event ever reported for Italy along with the 1693 eastern Sicily earthquake. The shock produced a large tsunami that caused severe damage and many victims. In all places the first sea movement was a withdrawal for a few minutes, followed by a flooding of the coast with at least three big waves. A post-event survey allowed to estimate flooding and run-up heights (more than 10 m in some places). In this work we perform some numerical simulations of the tsunami generation and propagation, taking into account different source faults: the model is based on the shallow water equations, solved numerically by means of a finiteelement method. The computational domain, covered by a mesh consisting of triangular elements, includes the Messina Straits and the sea facing the northeastern coast of Sicily and southern Calabria.

The 1693 earthquake was a disastrous event affecting eastern Sicily, southern Italy, where it caused over 60,000 victims and total destruction of several villages and towns in the districts of Siracusa, Ragusa, and Catania. The earthquake was followed by a tsunami that struck the Ionian coasts of Sicily and the Messina Strait and was probably observed even in the Aeolian Islands. Historical documents on sea waves and flooding, though not abundant, allow us to form a picture of the tsunami first attack and inundation. The first water movement all along the Sicilian coastline was a strong sea withdrawal, followed by a violent sea return and coastal flooding. The main purpose of this research is to put constraints on the focal mechanism of this earthquake on the basis of the available documents on the tsunami (1) by simulating tsunami from different possible sources via numerical modeling based on finite element technique and shallow water approximation and (2) by choosing the source best fitting the tsunami data as the most plausible cause for this tsunami. The relevance of this study should also be evaluated in light of the circumstance that no certain indication on the earthquake fault can be deduced from the available macroseismic data alone. Solving the source problem for this event, one of the largest occurring in southeastern Sicily in historical times, is a significant contribution to understanding the seismotectonic regime of the region and to assessing the related earthquake and tsunami hazard/risk with implications on mitigation policies.

A study of the historical tsunami that occurred on 30 July 1627 in Gargano, Apulia, southern Italy, has been conducted by performing numerical simulations based on integrating shallow water equations via a finite-element (FE) technique. The tsunami was generated by an I = XI earthquake which produced severe damage in the Gargano promontory. Macroseismic observations are not sufficient to determine, unambiguously, the epicentre and the generative fault position. In this study we have assumed a dip-slip focal mechanism which is known to be the most effective tsunami generation. Since the source location is uncertain, different simulations have been carried out assuming that the fault is placed on land (two cases) and offshore (two cases). The Adriatic basin facing the northern coast of Gargano has been covered by a triangle-based mesh, with triangle sizes adapted to the variable bathymetry, which proved to be advantageous in describing the irregular coastlines. The available historical observations concerning the tsunami are scarce and chiefly qualitative. Yet, comparing data with the results of the numerical simulations gives some important hints on the position of the genetic fault. Of all the sources studied, the one matching the observations better is the inshore fault causing the uplift of the sea block facing the Lesina lake. Accordingly, at the present stage of research, this fault can be assumed as that responsible for the 1627 earthquake and tsunami.

Southern Calabria is one of the Italian coastal regions mostly affected by tsunami hazard. This work is a part of a wider study of the assessment of the tsunami hazard in the southern Calabria and eastern Sicily. The tsunami which we focus our attention on was the first of a series of events that were associated with the 1783 Calabrian seismic crisis that was one of the most catastrophic affecting southern Italy in historical times. The tsunami was generated by an I=XI earthquake: the isoseismal field is elongated in the direction of the Apennine chain and centered in the Gioia Tauro plain where the most relevant damage was reported. Several numerical simulations of the tsunami have been performed by means of a finite-element method based on the shallow-water equations with different sources. The Tyrrhenian sea facing southern Calabria, including the Messina Strait, has been covered by a triangle-based mesh. The numerical results, compared with the available historical observations, such as the polarity of the first arriving wave, the mean wave period, etc. enable us to evaluate the most reliable source mechanisms and locations.

The 2 September 1992 Nicaragua tsunami was induced by an MS≃ 7–7.3 earthquake and caused about 170 victims and significant damage to the coastal areas. The aim of this work is to infer the slip distribution along the causative seismic fault from the available tsunami run-up field data. We have subdivided the fault plane into five slip-independent subfaults and computed the corresponding numerical Green's functions by integrating shallow-water equations via a finite-element technique. The slip distribution on the fault has been determined by applying a least-squares procedure to the differences between the observed run-up values and the computed maximum water levels along the coast. The main result is that the best fit is found for a nonuniform coseismic slip, with the highest displacement taking place in the southernmost part of the fault. The measure of the improvement is given by the global rms residual of the heterogeneous-slip case being circa 25% smaller than that of the uniform case. An ancillary outcome of the analysis is the evaluation of the mean amplification factor of the tsunami wave investing the Nicaraguan coast, that, on assuming a rigidity of 1×1010 N/m², results to be 3.45.

The 2011 Tohoku-oki (Mw 9.1) earthquake is so far the best-observed megathrust rupture, which allowed the collection of unprecedented offshore data. The joint inversion of tsunami waveforms (DART buoys, bottom pressure sensors, coastal wave gauges, and GPS-buoys) and static geodetic data (onshore GPS, seafloor displacements obtained by a GPS/acoustic combination technique), allows us to retrieve the slip distribution on a non-planar fault. We show that the inclusion of near-source data is necessary to image the details of slip pattern (maximum slip ~48 m, up to ~35 m close to the Japan trench), which generated the large and shallow seafloor coseismic deformations and the devastating inundation of the Japanese coast. We investigate the relation between the spatial distribution of previously inferred interseismic coupling and coseismic slip and we highlight the importance of seafloor geodetic measurements to constrain the interseismic coupling, which is one of the key-elements for long-term earthquake and tsunami hazard assessment.

[1] We study the 2003 Mw 8.1 Tokachi-oki earthquake, a great interplate event that occurred along the southwestern Kuril Trench and generated a significant tsunami. To determine the earthquake slip distribution, we perform the first joint inversion of tsunami waveforms measured by tide gauges and of coseismic displacement measured both by GPS stations and three ocean bottom pressure gauges (PG) for this event. The resolution of the different data sets on the slip distribution is assessed by means of several checkerboard tests. Results show that tsunami data constrain the slip distribution offshore, whereas GPS data constrain the slip distribution in the onshore zone. The three PG data only coarsely constrain the offshore slip, indicating that denser networks should be installed close to subduction zones. Combining the three data sets significantly improves the inversion results. Joint inversion of the 2003 Tokachi-oki earthquake data leads to maximum slip values (∼6 m) confined at depths greater than ∼25 km, between 30 and 80 km northwest of the hypocenter, with a patch of slip (3 m) in the deepest part of the source (∼50 km depth). Slip values are very low (≤1 m) updip from the hypocenter. Furthermore, the rupture does not extend on the plate interface off Akkeshi. As a significant back slip amount (∼4 m) has accumulated there since the last 1952 earthquake, this segment could rupture during the next large interplate event along the Kuril Trench.

[1] We (re)analyzed the source of the 26 December 2004 Sumatra-Andaman earthquake and tsunami through a nonlinear joint inversion of an inhomogeneous data set made up of tide gauges, satellite altimetry, and far-field GPS recordings. The purpose is twofold: (1) the retrieval of the main kinematics rupture parameters (slip, rake, and rupture velocity) and (2) the inference of the rigidity of the source zone. We independently estimate the slip from tsunami data and the seismic moment from geodetic data to derive the rigidity. Our results confirm that the source of the 2004 Sumatra-Andaman earthquake has a complex geometry, constituted by three main slip patches, with slip peaking at ∼30 m in the southern part of the source. The rake direction rotates counterclockwise at the northern part of the source, according to the direction of convergence along the trench. The rupture velocity is higher in the deeper than in the shallower part of the source, consistent with the expected increase of rigidity with depth. It is also lower in the northern part, consistent with known variations of the incoming plate properties and shear velocity. Our model features a rigidity (20–30 GPa) that is lower than the preliminary reference Earth model (PREM) average for the seismogenic volume. The source rigidity is one of the factors controlling the tsunami genesis: for a given seismic moment, the lower the rigidity, the higher the induced seafloor displacement. The general consistence between our source model and previous studies supports the effectiveness of our approach to the joint inversion of geodetic and tsunami data for the rigidity estimation.

We have quantified the effects of a water mass redistribution associated with the propagation of a tsunami wave on the Earths pole path and on the Length-Of-Day (LOD) and applied our modeling results to the tsunami following the 2004 giant Sumatra earthquake. We compared the result of our simulations on the instantaneous rotational axis variations with the preliminary instrumental evidence on the pole path perturbation (which has not been confirmed) registered just after the occurrence of the earthquake. The detected perturbation in the pole path showed a step-like discontinuity that cannot be attributed to the effect of a seismic dislocation. Our results show that the tsunami induced instantaneous rotational pole perturbation is indeed characterized by a step-like discontinuity compatible with the observations but its magnitude is almost one hundred times smaller than the detected one. The LOD variation induced by the water mass redistribution turns out to be not significant because the total effect is smaller than current measurements uncertainties.

[1] We image the rupture history of the 2007 Niigata-ken Chuestu-oki (Japan) earthquake by a nonlinear joint inversion of strong motion and GPS data, retrieving peak slip velocity, rupture time, rise time and slip direction. The inferred rupture model contains two asperities; a small patch near the nucleation and a larger one located 10 ÷ 15 km to the south-west. The maximum slip ranges between 2.0 and 2.5 m and the total seismic moment is 1.6 × 1019 Nm. The inferred rupture history is characterized by rupture acceleration and directivity effects, which are stable features of the inverted models. These features as well as the source-to-receiver geometry are discussed to interpret the high peak ground motions observed (PGA is 1200 gals) at the Kashiwazaki-Kariwa nuclear power plant (KKNPP), situated on the hanging-wall of the causative fault. Despite the evident source effects, predicted PGV underestimates the observed values at KKNPP by nearly a factor of 10.

Italian Civil Defense; Project “Development of new technologies for the protection of the Italian territory from natural hazards” funded by the Italian Ministry of University and Research