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The 2023 February 6 Mw 7.8 earthquake was the first one of a doublet which shook Türkiye and Syria causing, as per the estimates at the time of writing of this abstract, more than 45,000 casualties.The current standard operating procedures of the NEAMTWS (Tsunami Warning System in the North-Eastern Atlantic, the Mediterranean and connected seas, coordinated by UNESCO/IOC) for the initial tsunami warning message following an earthquake are based on a Decision Matrix (DM), whose input parameters are hypocentre and magnitude of the earthquake. Since the epicentre of this earthquake was located at a depth between 15-35 km at almost 100 km from the coast, both KOERI (Türkiye) and INGV (Italy) Tsunami Service Providers (TSPs) of the NEAMTWS issued a Tsunami Watch message (i.e., runup expected to exceed 1 m) for the whole Mediterranean Sea. NOA (Greece) did not issue any alert, because its initial location was more than 100 km from the coast.In response to the tsunami warning, trains were stopped in different locations in Southern Italy for several hours, and evacuation of some coastal areas was enforced. However, only a relatively small tsunami was recorded by Turkish close-by tide-gauges in the Eastern Mediterranean, with a maximum recorded amplitude of less than 50 cm. Based on these measurements and on others showing little to no tsunami at increasing distances, the alert was then ended after 5 and 9 hours by INGV and KOERI, respectively, based on the available tide-gauge recordings and interaction with Civil Protection Officers.This event has highlighted that NEAMTWS is an asset for the coastal communities. It can provide rapid alerts, which can save lives if the last-mile of the procedures is in place and the communities are “Tsunami Ready”, that is aware and prepared to respond with evacuations and other appropriate countermeasures. On the other hand, while it is reasonable – and dutiful based on current standard operation procedures – to issue a basin-wide, or at least a local alert, for an inland earthquake of unknown mechanism and of such a large magnitude, it is perhaps possible to improve the DM, which is totally heuristic and characterized by hard-thresholds, with consideration of numerical tsunami simulations and quantitative uncertainty treatment with more continuous variations. Moreover, there is no procedure currently in place to differentiate among locations where the expected time of arrival differs by many hours across the Mediterranean basin, nor a sufficient instrumental coverage that could make cancellation/ending faster due to a more solid observational basis.We will discuss some of the scientific and operational aspects with the aim of identifying which lessons can be learned to improve the NEAMTWS efficiency. We will also compare the DM-based alerts with those that would be produced with the recently introduced Probabilistic Tsunami Forecasting (PTF, Selva et al., 2021, Nature Communications), presently in pre-operational testing at INGV.

Subduction zones are the most seismically active regions in the world and hosted many great tsunamigenic earthquakes in the past, often with destructive coastal consequences. Hence, an accurate estimate of the tsunami forecast is crucial in Tsunami Early Warning Systems (TEWS) framework. However, the inherent uncertainties associated with the tsunami source estimation in real-time make tsunami forecasting challenging. In this study, we consider the South American subduction zone, where in the last 15 years occurred, three M8+ tsunamigenic earthquakes; in particular, we focus on the 2014 Mw 8.1 Iquique event.Here, we evaluate the variability of the tsunami forecasting for the Chilean coast as resulting i) from the coseismic slip model obtained by geophysical data inversion and ii) from an expeditious method for the tsunami source estimation, based on an extension of the well-known spectral approach. In the former method, we estimate the slip distribution of the 2014 Iquique earthquake by jointly inverting tsunami (DARTs and tide-gauges) and GPS data; we adopt a 3D fault geometry and Green’s functions approach.On the other hand, a set of stochastic slip models in the latter is generated through a Phase Variation Method (PVM), where realizations are obtained from both the wavenumber and phase spectra of the source.In the analysis, we also evaluate how the different physics complexity included in the tsunami modelling (e.g. by including dispersion or not) can be mapped into the tsunami forecasting uncertainty. Finally, as an independent check, we compare the predicted deformation field from the slip models (inverted or by PVM) with the RADARSAT-2 InSAR data.

The Istituto Nazionale di Geofisica e Vulcanologia (INGV) has the primary responsibility for the seismic surveillance service of the Italian territory and the tsunami alert in the Mediterranean Sea.The activities in the monitoring room at the INGV National Earthquake Observatory headquarters in Rome (hereafter INGV-Rome), are carried on by two seismologists, one tsunami specialist and one technician/engineer who work in three shifts a day to provide monitoring service on a 24/7 basis. They calculate, as rapidly and accurately as possible, the location and size of all Italian earthquakes with M2.5+ and swiftly disseminate such information to emergency authorities, to government agencies, to the public and the media by different platforms (email, text message, and via Facebook and Twitter). Starting with hypocentral and magnitude parameters, the moment tensors, the historical seismicity map and the shakemaps are also published in (near) real time.In addition, the INGV-Rome monitoring room hosts the Italian Tsunami Alert Center (CAT-INGV). CAT-INGV is one of the Tsunami Service Providers acting in the North-eastern Atlantic, the Mediterranean and connected sea (NEAM) region of the Intergovernmental Oceanographic Commission (IOC)/UNESCO and is responsible for monitoring the seismicity of the Mediterranean Sea and disseminating tsunami alert messages to member States and EU agencies subscribing its services. The operation and the performance of the INGV monitoring system is ensured by a dedicated research and IT staff who facilitate real-time waveform acquisition and distribution, develop real-time seismic processing systems and new processing algorithms., The 28th IUGG General Assembly (IUGG2023) (Berlin 2023)

The accurate estimate of the tsunami forecast is crucial in Tsunami Early Warning Systems (TEWS) framework. However, the inherent uncertainties associated with the tsunami source estimation in real-time make tsunami forecasting challenging.In this study, we consider the South American subduction zone, one of the most seismically active regions in the world, where in the last 15 years occurred, three M8+ tsunamigenic earthquakes; in particular, we focus on the 2014 Mw 8.1 Iquique event.Here, we compare the tsunami forecasting for the Chilean coast as resultingi)from the coseismic slip model obtained by geophysical data inversion andii)from an expeditious method for the tsunami source estimation, based on an extension of the well-known spectral approach.In the former method, we estimate the slip distribution of the 2014 Iquique earthquake by jointly inverting tsunami waveforms and GPS data; on the other hand, a set of stochastic slip models in the latter is generated through a Phase Variation Method (PVM), where realizations are obtained from both the wavenumber and phase spectra of the source.We also evaluate how the different physics complexity included in the tsunami modelling (e.g. by including dispersion or not) can be mapped into the tsunami forecasting uncertainty. Finally, as an independent check, we compare the predicted deformation field from the slip models (inverted or by PVM) with the RADARSAT-2 InSAR data., The 28th IUGG General Assembly (IUGG2023) (Berlin 2023)

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)

We present a source solution for the tsunami generated by the Mw 6.6 earthquake that occurred on 2 May 2020, about 80 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 and Kasos island. We used Crete 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 Ierapetra observed marigram 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 in the framework of both the long-term hazard assessment and the early warning systems.

Destructive tsunamis are most often generated by large earthquakes occurring at subduction interfaces, but also other “atypical” sources—defined as crustal earthquakes and non-seismic sources altogether—may cause significant tsunami threats. Tsunamis may indeed be generated by different sources, such as earthquakes, submarine or coastal landslides, volcano-related phenomena, and atmospheric perturbations. The consideration of atypical sources is important worldwide, but it is especially prominent in complex tectonic settings such as the Mediterranean, the Caribbean, or the Indonesian archipelago. The recent disasters in Indonesia in 2018, caused by the Palu-Sulawesi magnitude Mw 7.5 crustal earthquake and by the collapse of the Anak-Krakatau volcano, recall the importance of such sources. Dealing with atypical sources represents a scientific, technical, and computational challenge, which depends on the capability of quantifying and managing uncertainty efficiently and of reducing it with accurate physical modelling. Here, we first introduce the general framework in which tsunami threats are treated, and then we review the current status and the expected future development of tsunami hazard quantifications and of the tsunami warning systems in Italy, with a specific focus on the treatment of atypical sources. In Italy, where the memory of historical atypical events like the 1908 Messina earthquake or the relatively recent 2002 Stromboli tsunami is still vivid, specific attention has been indeed dedicated to the progressive development of innovative strategies to deal with such atypical sources. More specifically, we review the (national) hazard analyses and their application for coastal planning, as well as the two operating tsunami warning systems: the national warning system for seismically generated tsunamis (SiAM), whose upstream component—the CAT-INGV—is also a Tsunami Service Provider of the North-eastern Atlantic, the Mediterranean and connected seas Tsunami Warning System (NEAMTWS) coordinated by the Intergovernmental Coordination Group established by the Intergovernmental Oceanographic Commission (IOC) of UNESCO, and the local warning system for tsunamis generated by volcanic slides along the Sciara del Fuoco of Stromboli volcano. Finally, we review the state of knowledge about other potential tsunami sources that may generate significant tsunamis for the Italian coasts, but that are not presently considered in existing tsunami warning systems. This may be considered the first step towards their inclusion in the national tsunami hazard and warning programs.

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.

Increasingly, economies that have traditionally benefited from offshoring are losing some of their strategical advantages, with a consequent increase in backshoring by developed economies. This paper describes the phenomenon and tries to shed light on the current challenges, trends, and debates in the area, and on the main determinants of backshoring. A new phenomenon known as nearshoring is also analysed—this consists of relocating some previously offshored manufacturing activities so that they are now close to previous core locations, but not so close as to suffer from disagglomeration effects. This combines the advantages of offshoring and backshoring.

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.

X Congreso Geológico de España, 5-7 de julio 2021, Vitoria-Gasteiz.-- 1 page, [EN] The SW Iberian margin is one of the most seismogenic and tsunamigenic areas in Western Europe, where large historical and instrumental destructive earthquakes and tsunamis have occurred. For this reason, we present a new study to evaluate the sensitivity of the tsunami impact on the coast of SW Iberia and NW Morocco to the fault geometry and slip distribution for local earthquakes. We carried out several tsunami simulations considering the detailed geometry of the main active faults in the region: the Gorringe Bank (GBF), Marquês de Pombal (MPF), Horseshoe (HF), North Coral Patch (NCPF) and South Coral Patch (SCPF) thrust faults, and the Lineament South (LSF) strike-slip fault. We started from relatively simple planar faults featuring uniform slip for all faults; then, based on a large dataset of 2D multi-channel seismic profiles, 3D complex sub-surface models of the fault planes (MPF, HF, NCPF, and SCPF) have been generated. Finally, we used several heterogeneous slip-distributions for the HF case. Our tsunami models suggest that using more complex fault geometries and heterogeneous slip distributions, the peak wave height (about the sea level) at the coastline can be doubled compared to simpler tsunami source scenarios generated by simple fault-plane geometries, [ES] El margen SO de la Península Ibérica es una de las zonas más sismogénicas y tsunamigénicas de Europa Occidental, donde han ocurrido grandes terremotos y tsunamis destructivos, tanto en periodo histórico como instrumental. Por este motivo, presentamos un nuevo estudio evaluando la sensibilidad de los escenarios de tsunamis a la geometría de los planos de falla y la distribución del deslizamiento aplicado a las costas del SO de Iberia y del NE de Marruecos. En este trabajo realizamos diversas simulaciones de tsunami considerando la geometría en detalle de las principales fallas activas de la región, incluyendo: las fallas inversas de Gorringe Bank (GBF), Marquês de Pombal (MPF), Horseshoe (HF), North Coral Patch (NCPF) y South Coral Patch (SCPF); y la falla transcurrente del Lineament South (LSF). Empezamos considerando planos de falla simples con deslizamiento uniforme para todas las fallas. A continuación, generamos modelos complejos en 3D de los planos de falla para MPF, HF, NCPF y SCPF en base a un gran conjunto de datos de perfiles de sísmica multicanal 2D. Finalmente, utilizamos varias distribuciones de deslizamiento heterogéneo para el caso de HF. Nuestros modelos de tsunami sugieren que utilizando geometrías de falla complejas y distribuciones de deslizamiento heterogéneas, la altura máxima de la ola (sobre el nivel del mar) en la costa se puede duplicar en comparación con escenarios simples, dónde el tsunami es generado por una falla con geometría planar

L'INGV è Centro di Competenza per i fenomeni sismici, vulcanici e i maremoti per il Dipartimento di Protezione Civile Nazionale (DPC). Nell’ambito delle attività previste dall’Accordo Quadro DPC-INGV 2012-2021 (AQ vigente), l’INGV svolge attività di sorveglianza tecnico-scientifica sulla sismicità del territorio nazionale, sui fenomeni vulcanici e sui maremoti, finalizzata ai compiti di protezione civile, in modo ininterrotto (H24 per 365 giorni l’anno). Tale attività viene realizzata con uno specifico assetto organizzativo, che consente la trasmissione in tempo reale verso il DPC di tutte le informazioni riguardanti eventi e rischi sismici, vulcanici e da maremoto di interesse per il Dipartimento stesso. La sorveglianza sismica del territorio nazionale e delle aree limitrofe è in carico all’Osservatorio Nazionale Terremoti (ONT), insieme alle comunicazioni relative agli eventi in area mediterranea e nel mondo. La sorveglianza delle aree vulcaniche campane (Campi Flegrei, Ischia, Vesuvio) e siciliane (Etna, Stromboli, Vulcano, altre isole Eolie, Pantelleria) sono rispettivamente in carico all’Osservatorio Vesuviano (OV) e all’Osservatorio Etneo (OE). Dal gennaio 2017 è diventata ufficialmente operativa anche l’attività di monitoraggio e il Servizio di allerta dei maremoti di origine sismica (Centro Allerta Tsunami - CAT) con l’introduzione nella Sala INGV di Roma di una nuova unità di personale. In fase sperimentale, fino alla fine del 2016, e per i primi mesi di operatività, il personale per il Servizio di Allerta Tsunami è stato scelto all’interno del gruppo di turnisti che da anni svolgeva il Servizio di Sorveglianza Sismica; successivamente, è stato reclutato e formato nuovo personale in grado di svolgere entrambi i Servizi. A partire dal 2017 e nei due anni successivi sono stati attivati, quindi, i corsi per la formazione di nuovi turnisti e funzionari per i servizi di Sorveglianza Sismica e di Allerta Tsunami ed anche per i reperibili di Sala [Quintiliani et al., 2020]. La formazione del personale che partecipa al Servizio di Sorveglianza Sismica è prevista nei Piani di attività annuali relativi all’Allegato A dell’AQ vigente, tematica “Sorveglianza sismica” e quella del personale che partecipa alle attività del CAT nella tematica “Centro Allerta Tsunami (CAT)”. Inoltre, il Progetto “S.O.I.R. monitoraggio futuro” ha tra le sue finalità quella della formazione del personale delle Sale Operative INGV, essendo il WP4 “Formazione” uno dei sei working package del progetto espressamente dedicato a questo.

Finite-fault models for the 2010Mw8.8 Maule, Chile earthquake indicate bilateral rupture with large-slip patches located north and south of the epicenter. Previous studies also show that this event features significant slip in the shallow part of the megathrust, which is revealed through correction of the forward tsunami modeling scheme used in tsunami inversions. The presence of shallow slip is consistent with the coseismic seafloor deformation measured off the Maule region adjacent to the trench and confirms that tsunami observations are particularly important for constraining far-offshore slip. Here, we benchmark the method of Optimal Time Alignment (OTA) of the tsunami waveforms in the joint inversion of tsunami (DART and tide-gauges) and geodetic (GPS, InSAR, land-leveling) observations for this event. We test the application of OTA to the tsunami Green’s functions used in a previous inversion. Through a suite of synthetic tests we show that if the bias in the forward model is comprised only of delays in the tsunami signals, the OTA can correct them precisely, independently of the sensors (DART or coastal tide-gauges) and, to the first-order, of the bathymetric model used. The same suite of experiments is repeated for the real case of the 2010 Maule earthquake where, despite the results of the synthetic tests, DARTs are shown to outperform tide-gauges. This gives an indication of the relative weights to be assigned when jointly inverting the two types of data. Moreover, we show that using OTA is preferable to subjectively correcting possible time mismatch of the tsunami waveforms. The results for the source model of the Maule earthquake show that using just the first-order modeling correction introduced by OTA confirms the bilateral rupture pattern around the epicenter, and, most importantly, shifts the inferred northern patch of slip to a shallower position consistent with the slip models obtained by applying more complex physics-based corrections to the tsunami waveforms. This is confirmed by a slip model refined by inverting geodetic and tsunami data complemented with a denser distribution of GPS data nearby the source area. The models obtained with the OTA method are finally benchmarked against the observed seafloor deformation off the Maule region. We find that all of the models using the OTA well predict this offshore coseismic deformation, thus overall, this benchmarking of the OTA method can be considered successful.

On 28 September 2018 a Mw 7.5 strike-slip earthquake occurred on the Palu-Koro fault system in the Sulawesi Island. Immediately after the earthquake a powerful tsunami hit the Palu Bay causing large damages and numerous fatalities.Several works, inverting seismic or geodetic data, clearly estimated the slip distribution of this event, but the causative source of the tsunami is still not completely understood; indeed, the strike-slip mechanism of the seismic source alone might not be sufficient to explain the large runups observed (> 6 m) along the coast of the Palu Bay, and thus one or more additional non-seismic sources like a landslide could have contributed to generate the big tsunami. An insight of that can be found in an extraordinary collection of amateur videos, and on the only available tide gauge in the Bay, at Pantoloan, that showed evidence for a short period wave of at least 2-3 minutes, compatible with a landslide.In this study, we attempt to discriminate the contribution in the tsunami generation of both the seismic source and some supposed landslides distributed along the coast of the Bay.In particular, we attempt to estimate the causative source of the tsunami by means of a nonlinear joint inversion of geodetic (InSAR) and runup data. We use a fault geometry consistent with the Sentinel-2 optical analysis results and analytically compute the geodetic Green’s functions. The same fault model is used to compute the initial condition for the seismic tsunami Green’s functions, including the contribution of the horizontal deformation due to the gradient of the bathymetry (10 m spatial resolution); the landslide tsunami Green’s functions are computed the software BingClaw by placing several hypothetical sources in the Bay. In both the cases the tsunami propagation is modelled by numerically solving the nonlinear shallow water equations.In this work we also attempt to address the validity of Green’s functions approach (linearity) for earthquake and landslide sources as well as the wave amplitude offshore as predictor of nearby runup.