Arrival angles of teleseismic fundamental mode Rayleigh waves across the AlpArray

The dense AlpArray network allows studying seismic wave propagation with high spatial resolution. Here we introduce an array approach to measure arrival angles of teleseismic Rayleigh waves. The approach combines the advantages of phase correlation as in the two-station method with array beamforming to obtain the phase-velocity vector. 20 earthquakes from the first two years of the AlpArray project are selected, and spatial patterns of arrival-angle deviations across the AlpArray are shown in maps, depending on period and earthquake location. The cause of these intriguing spatial patterns is discussed. A simple wave-propagation modelling example using an isolated anomaly and a Gaussian beam solution suggests that much of the complexity can be explained as a result of wave interference after passing a structural anomaly along the wave paths. This indicates that arrival-angle information constitutes useful additional information on the Earth structure, beyond what is currently used in inversions

Ambient-noise tomography of the wider Vienna Basin region

We present a new 3-D shear-velocity model for the top 30 km of the crust in the wider Vienna Basin region based on surface waves extracted from ambient-noise cross-correlations. We use continuous seismic records of 63 broad-band stations of the AlpArray project to retrieve interstation Green’s functions from ambient-noise cross-correlations in the period range from 5 to 25 s. From these Green’s functions, we measure Rayleigh group traveltimes, utilizing all four components of the cross-correlation tensor, which are associated with Rayleigh waves (ZZ, RR, RZ and ZR), to exploit multiple measurements per station pair. A set of selection criteria is applied to ensure that we use high-quality recordings of fundamental Rayleigh modes. We regionalize the interstation group velocities in a 5 km × 5 km grid with an average path density of ∼20 paths per cell. From the resulting group-velocity maps, we extract local 1-D dispersion curves for each cell and invert all cells independently to retrieve the crustal shear-velocity structure of the study area. The resulting model provides a previously unachieved lateral resolution of seismic velocities in the region of ∼15 km. As major features, we image the Vienna Basin and Little Hungarian Plain as low-velocity anomalies, and the Bohemian Massif with high velocities. The edges of these features are marked with prominent velocity contrasts correlated with faults, such as the Alpine Front and Vienna Basin transfer fault system. The observed structures correlate well with surface geology, gravitational anomalies and the few known crystalline basement depths from boreholes. For depths larger than those reached by boreholes, the new model allows new insight into the complex structure of the Vienna Basin and surrounding areas, including deep low-velocity zones, which we image with previously unachieved detail. This model may be used in the future to interpret the deeper structures and tectonic evolution of the wider Vienna Basin region, evaluate natural resources, model wave propagation and improve earthquake locations, among others

Building an efficient and inclusive communication strategy for risk reduction in Haiti through a citizen-seismology approach

International audienceOn January 12th 2010, Haiti was hit by one of the largest seismic disasters known to date. At the time, seismic sensors, knowledge and risk culture were critically lacking. The dramatic social, political and economic consequences of the event revealed the importance of developing seismic risk reduction in Haiti. We present here the communication components of a citizen-seismology project in Haiti.. The project called OSMOSE propose to contribute to risk reduction by in installing low-cost seismic sensors (Raspberry Shake) at volunteers' houses to (1) collect seismic data and complement the national seismic network, and (2) engage with the population to understand their risk perception and the usage they could make of these tools. An international team of geoscientists, education specialists and social science researchers gathered to build an efficient communication strategy, which aimed at (1) informing the public about seismic risk and felt earthquakes, (2) establish a trust relationship with volunteers who host sensors, educate them about science and risk, (3) support the volunteers in their ambassador roles among their community. In order to establish a communication strategy that was inclusive and suitable to the local cultural context (including scientific literacy level, vodou culture, risk culture, past trauma, trust in the authorities etc), we first led a quantitative survey among the general public and a series of sociological semi-structured interviews with Raspberry Shake hosts who volunteered for the project. This enabled us to assess information expectations in terms of content and medium. Working with geoscientists, we then designed a first set of tools to respond to these needs, when possible. For instance, a website (https://ayiti.unice.fr/ayiti-seismes/) enables the public to know in a few minutes where an earthquake occurs and what its magnitude is, thanks to seismic data collected by the citizen network. It also displays educational information about seismology. The LastQuake app which crowdsources seismic data was translated into Creole for better access in the country. Finally, a WhatsApp group gathering volunteers and scientists has also been created given the importance of the messaging app in daily communication and information practices in Haiti. The group enables them to exchange information about the technical and scientific aspects of the Raspberry Shake they host and data they collect. During the August 14th 2021 earthquake, the group was used to share information about damage and rumors. Yet, this communication strategy is still incomplete and requires improvements. For instance, volunteers requested pedagogical support to better play their ambassador role among their community. Communication towards the general public also needs to gain visibility and accessibility. As part of an iterative process, additional interviews and assessment will help us improve the communication strategy. We will also include additional partners (such as schools, disaster management institutions, etc.) and test other methods such as a Virtual Reality tool. We argue not only that assessing the public needs is essential to build an inclusive and efficient communication strategy but also that the citizen-science approach is a strong asset to achieve this goal