Irene Molinari

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Molinari

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Irene

ORCID

0000-0002-8314-1444

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Publications 1 - 10 of 14

Facilitating Multi-Disciplinary Research via Integrated Access to the Seismological Data & Product Services of EPOS Seismology
Haslinger, Florian; Ottemöller, Lars; Cauzzi, Carlo Virgilio; et al. (2022)
EGUsphere
The European Plate Observing System EPOS is the single coordinated framework for solid Earth science data, products and services on a European level. As one of the science domain structures within EPOS, EPOS Seismology brings together the three large European infrastructures in seismology: ORFEUS for seismic waveform data & related products, EMSC for parametric earthquake information, and EFEHR for seismic hazard and risk information. Across these three pillars, EPOS Seismology provides services to store, discover and access seismological data and products from raw waveforms to elaborated hazard and risk assessment. ORFEUS, EMSC and EFEHR are community initiatives / infrastructures that each have their own history, structure, membership, governance and established mode of work (including data sharing and distribution practices), developed in parts over decades. While many institutions and individuals are engaged in more than one of these initiatives, overall the active membership is quite distinct. Also, each of the initiatives has different connections to and interactions with other international organisations. Common to all is the adoption and promotion of recognized international standards for data, products and services originating from wider community organisations (e.g. FDSN, IASPEI, GEM), and the active participation in developing those further or creating new ones together with the community. In this presentation we will briefly review the history and development of the three initiatives and discuss how we set up EPOS Seismology as a joint coordination framework within EPOS. We will highlight issues encountered on the way and those that we are still trying to solve in our attempt to create and operate a coordinated research infrastructure that appropriately serves the needs of today’s scientific community. Among those issues is also the ‘timeliness’ of data and products: while a number of services offer almost-real-time access to newly available information at least in theory, this comes with various downstream implications that are currently actively discussed. We also cover the envisaged role of EPOS Seismology in supporting international multi-disciplinary activities that require and benefit from harmonized, open, and interoperable data, products, services and facilities from the waveform, catalogue and hazard / risk domains of seismology.
3D crustal structure of the Eastern Alpine region from ambient noise tomography
Molinari, Irene; Obermann, Anne; Kissling, Eduard; et al. (2020)
Results in Geophysical Sciences
The tectonic evolution of the European Eastern Alps within the Alpine orogeny is still under debate. Open questions include: the link between surface, crustal and mantle structures; the nature of the Moho gap between the two plates; the relationship between the Alps, the adjacent foreland basin and the Bohemian Massif lithospheric blocks. We collected one year of continuous data recorded by ~250 broadband seismic stations –55 of which installed within the EASI AlpArray complementary experiment– in the Eastern Alpine region. Exploiting surface wave group velocity from seismic ambient noise, we obtained an high-resolution 3D S-wave crustal model of the area. The Rayleigh-wave group-velocity from 3 s to 35 s are inverted to obtain 2-D group velocity maps with a resolution of ~15 km. From these maps, we determine a set of 1D velocity models via a Neighborhood Algorithm, resulting in a new 3D model of S-wave velocity with associated uncertainties. The vertical parameterization is a 3-layer crust with the velocity properties in each layer described by a gradient. Our final model finds high correlation with specific geological features in the Eastern Alps up to 20 km depth, the deep structure of the Molasse basin and important variations of crustal thickness and velocities as a result of the Alpine orogeny post-collisional evolution. The strength of our new information relies on the absolute S-wave crustal velocity and the velocity gradient unambiguously sampled along the Moho, only limited by the amount and quality distribution of the data available.
Fast evaluation of tsunami scenarios: uncertainty assessment for a Mediterranean Sea database
Molinari, Irene; Tonini, Roberto; Lorito, Stefano; et al. (2016)
Natural Hazards and Earth System Sciences
We present a database of pre-calculated tsunami waveforms for the entire Mediterranean Sea, obtained by numerical propagation of uniformly spaced Gaussian-shaped elementary sources for the sea level elevation. Based on any initial sea surface displacement, the database allows the fast calculation of full waveforms at the 50m isobath offshore of coastal sites of interest by linear superposition. A computationally inexpensive procedure is set to estimate the coefficients for the linear superposition based on the potential energy of the initial elevation field. The elementary sources size and spacing is fine enough to satisfactorily reproduce the effects of M> = 6.0 earthquakes. Tsunami propagation is modelled by using the Tsunami-HySEA code, a GPU finite volume solver for the non-linear shallow water equations. Like other existing methods based on the initial sea level elevation, the database is independent on the faulting geometry and mechanism, which makes it applicable in any tectonic environment. We model a large set of synthetic tsunami test scenarios, selected to explore the uncertainty introduced when approximating tsunami waveforms and their maxima by fast and simplified linear combination. This is the first time to our knowledge that the uncertainty associated to such a procedure is systematically analysed and that relatively small earthquakes are considered, which may be relevant in the near-field of the source in a complex tectonic setting. We find that non-linearity of tsunami evolution affects the reconstruction of the waveforms and of their maxima by introducing an almost unbiased (centred at zero) error distribution of relatively modest extent. The uncertainty introduced by our approximation can be in principle propagated to forecast results. The resulting product then is suitable for different applications such as probabilistic tsunami hazard analysis, tsunami source inversions and tsunami warning systems.
Structure of Masaya and Momotombo volcano, Nicaragua, investigated with a temporary seismic network
Obermann, Anne; Molinari, Irene; Métaxian, Jean-Philippe; et al. (2019)
Journal of Volcanology and Geothermal Research
Source of the 6 February 2013 M-w=8.0 Santa Cruz Islands Tsunami
Romano, Fabrizio; Molinari, Irene; Lorito, Stefano; et al. (2015)
Natural Hazards and Earth System Sciences
On 6 February 2013 an Mw = 8.0 subduction earthquake occurred close to Santa Cruz Islands at the transition between the Solomon and the New Hebrides Trench. The ensuing tsunami caused significant inundation on the closest Nendo Island. The seismic source was studied with teleseismic broadband P-wave inversion optimized with tsunami forward modelling at DART buoys (Lay et al., 2013) and with inversion of teleseismic body and surface waves (Hayes et al., 2014a). The two studies also use different hypocentres and different planar fault models and found quite different slip models. In particular, Hayes et al. (2014a) argued for an aseismic slip patch SE from the hypocentre. We here develop a 3-D model of the fault surface from seismicity analysis and retrieve the tsunami source by inverting DART and tide-gauge data. Our tsunami source model features a main slip patch (peak value of ~ 11 m) SE of the hypocentre and reaching the trench. The rake direction is consistent with the progressively more oblique plate convergence towards the Solomon trench. The tsunami source partially overlaps the hypothesized aseismic slip area, which then might have slipped coseismically.
Azimuthal anisotropy from eikonal tomography: example from ambient-noise measurements in the AlpArray network
Kästle, Emanuel David; Molinari, Irene; Boschi, Lapo; et al. (2022)
Geophysical Journal International
Ambient-noise records from the AlpArray network are used to measure Rayleigh wave phase velocities between more than 150 000 station pairs. From these, azimuthally anisotropic phase-velocity maps are obtained by applying the eikonal tomography method. Several synthetic tests are shown to study the bias in the Ψ2 anisotropy. There are two main groups of bias, the first one caused by interference between refracted/reflected waves and the appearance of secondary wave fronts that affect the phase traveltime measurements. This bias can be reduced if the amplitude field can be estimated correctly. Another source of error is related to the incomplete reconstruction of the traveltime field that is only sparsely sampled due to the receiver locations. Both types of bias scale with the magnitude of the velocity heterogeneities. Most affected by the spurious Ψ2 anisotropy are areas inside and at the border of low-velocity zones. In the isotropic velocity distribution, most of the bias cancels out if the azimuthal coverage is good. Despite the lack of resolution in many parts of the surveyed area, we identify a number of anisotropic structures that are robust: in the central Alps, we find a layered anisotropic structure, arc-parallel at mid-crustal depths and arc-perpendicular in the lower crust. In contrast, in the eastern Alps, the pattern is more consistently E–W oriented which we relate to the eastward extrusion. The northern Alpine forleand exhibits a preferential anisotropic orientation that is similar to SKS observations in the lowermost crust and uppermost mantle.
Coordinated and Interoperable Seismological Data and Product Services in Europe: the EPOS Thematic Core Service for Seismology
Haslinger, Florian; Basili, Roberto; Bossu, Rémy; et al. (2022)
Annals of Geophysics
In this article we describe EPOS Seismology, the Thematic Core Service consortium for the seismology domain within the European Plate Observing System infrastructure. EPOS Seismology was developed alongside the build-up of EPOS during the last decade, in close collaboration between the existing pan-European seismological initiatives ORFEUS (Observatories and Research Facilities for European Seismology), EMSC (Euro-Mediterranean Seismological Center) and EFEHR (European Facilities for Earthquake Hazard and Risk) and their respective communities. It provides on one hand a governance framework that allows a well-coordinated interaction of the seismological community services with EPOS and its bodies, and on the other hand it strengthens the coordination among the already existing seismological initiatives with regard to data, products and service provisioning and further development. Within the EPOS Delivery Framework, ORFEUS, EMSC and EFEHR provide a wide range of services that allow open access to a vast amount of seismological data and products, following and implementing the FAIR principles and supporting open science. Services include access to raw seismic waveforms of thousands of stations together with relevant station and data quality information, parametric earthquake information of recent and historical earthquakes together with advanced event-specific products like moment tensors or source models and further ancillary services, and comprehensive seismic hazard and risk information, covering latest European scale models and their underlying data. The services continue to be available on the well-established domain-specific platforms and websites, and are also consecutively integrated with the interoperable central EPOS data infrastructure. EPOS Seismology and its participating organizations provide a consistent framework for the future development of these services and their operation as EPOS services, closely coordinated also with other international seismological initiatives, and is well set to represent the European seismological research infrastructures and their stakeholders within EPOS.
Inferring Crustal Temperatures Beneath Italy From Joint Inversion of Receiver Functions and Surface Waves
Cammarano, Fabio; Nicola, Piana Agostinetti; Gao, Chao; et al. (2019)
Journal of Geophysical Research: Solid Earth
A simple method for earthquake location by surface-wave time reversal
Boschi, Lapo; Molinari, Irene; Reinwald, Michael (2018)
Geophysical Journal International
The scalar 2-D Helmholtz equation (i.e. ‘membrane waves’) can be used to model surface-wave propagation in a laterally smooth, lossless half-space. Building on this known result, we develop an algorithm to localize earthquake sources based on surface-wave data, via numerical time reversal on a membrane, where monochromatic waves propagate with the phase velocity of Rayleigh or Love waves at the same frequency. By conducting monochromatic membrane-wave time-reversal simulations at various frequencies and combining the results, broad-band time-reversed surface waves can be modelled. Importantly, membrane-wave modelling is computationally much less expensive than 3-D surface-wave modelling. We first explain rigorously the relationship between surface waves and membrane waves. Our mathematical treatment is slightly different from those found in the literature, in that it does not invoke variational principles. We next implement our time-reversal algorithm via spectral elements as well as simple ray tracing. Both implementations account for the effects of lateral variations in phase velocity. We validate the two resulting tools by means of several numerical experiments. This includes synthetic tests, as well as the localization of a virtual source based on a data set of real ambient-noise cross-correlations, and the localization of the epicentre of a real earthquake from real, raw data. In this study, applications are limited to northern Italy and the Alpine arc, where we have access to recent, high-resolution phase velocity maps, ambient-noise cross-correlations and data from a recent, relatively large earthquake. The accuracy of epicentre location despite non-uniformity in station coverage encourages further applications of our method, in particular to the task of mapping large-earthquake rupture in space and time.
Swiss-AlpArray temporary broadband seismic stations deployment and noise characterization
Molinari, Irene; Clinton, John Francis; Kissling, Eduard; et al. (2016)
Advances in Geosciences
AlpArray is a large collaborative seismological project in Europe that includes more than 50 research institutes and seismological observatories. At the heart of the project is the collection of top-quality seismological data from a dense network of broadband temporary seismic stations, in compliment to the existing permanent networks, that ensures a homogeneous station coverage of the greater Alpine region. This Alp Array Seismic Network (AASN) began operation in January 2016 and will have a duration of at least 2 years. In this work we report the Swiss contribution to the AASN, we concentrate on the site selection process, our methods for stations installation, data quality and data management. We deployed 27 temporary broadband stations equipped with STS-2 and Trillium Compact 120s sensors. The deployment and maintenance of the temporary stations across 5 countries is managed by ETH Zurich and it is the result of a fruitful collaboration between five institutes in Europe.

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