Download the PACIFIC project presentation https://www.pacific-h2020.eu/wp-content/uploads/PACIFIC-Project-presentation.pdf 

Executive summary: A key goal of the PACIFIC project is to develop methodologies for the extraction of body waves from passive seismic data, for use in the environmentally sustainable environments. Recovering body waves from ambient noise data has proved to be challenging as they are usually weak and ambient noise fields are rich in surface waves. Here we propose and test a method, based on the Radon Transformation, that helps suppress surface waves and enhance reflected body waves. The method exploits the ‘moveout’ differences between reflected body (hyperbolic) and surface waves (linear) and is tested on synthetic 2D & 3D model data prior to its application to ambient noise field data. We refer to it as Radon Correlation. Synthetic tests are very encouraging, showing clear body wave recovery that cannot be seen in raw cross-correlated data. Using these synthetics to have a choice of parameters, we then move to field passive data from the Marathon site within PACIFIC. We generate virtual shot gathers by applying Radon Correlation to single virtual sources into a linear array of receivers. Again, results are very encouraging with clear reflected body wave recovery from the ambient noise data and determined by clear hyperbolic arrivals on the virtual shot gathers. There is a hint that using time windows that contain active blast seismic coda possibly further enhances body wave recovery. Finally, velocity analysis on these virtual shot gathers leads to a P-wave velocity model that compares well with models derived from surface wave dispersion analysis of the same ambient noise data. However, these models are not currently publicly available and hence are not shown here, in this report.

Ambient noise multimode Rayleigh and Love wave tomography to determine the shear velocity structure above the Groningen gas field

The Groningen gas field is one of the largest gas fields in Europe. The continuous gas extraction led to an induced seismic activity in the area. In order to monitor the seismic activity and study the gas field many permanent and temporary seismic arrays were deployed. In particular, the extraction of the shear wave velocity model is crucial in seismic hazard assessment. Local S-wave velocity-depth profiles allow us the estimation of a potential amplification due to soft sediments.

Ambient seismic noise tomography is an interesting alternative to traditional methods that were used in modelling the S-wave velocity. The ambient noise field consists mostly of surface waves, which are sensitive to the Swave and if inverted, they reveal the corresponding S-wave structures.

In this study, we present results of a depth inversion of surface waves obtained from the cross-correlation of 1 month of ambient noise data from four flexible networks located in the Groningen area. Each block consisted of about 400 3-C stations. We compute group velocity maps of Rayleigh and Love waves using a straight-ray surface wave tomography. We also extract clear higher modes of Love and Rayleigh waves.

The S-wave velocity model is obtained with a joint inversion of Love and Rayleigh waves using the Neighbourhood Algorithm. In order to improve the depth inversion, we use the mean phase velocity curves and the higher modes of Rayleigh and Love waves. Moreover, we use the depth of the base of the North Sea formation as a hard constraint. This information provides an additional constraint for depth inversion, which reduces the S-wave velocity uncertainties.

The final S-wave velocity models reflect the geological structures up to 1 km depth and in perspective can be used in seismic risk modelling.

Executive summary: The Winter School on Sustainable Mineral Exploration was jointly organized by two European projects—PACIFIC and INFACT. The event was held at the International Campus of Andalusia in Huelva, Spain, between the 9th and 12th March 2020. The Winter School was divided in 3 lecture sessions, 1 practical session, and 2 visits to mining sites. The main goal of this school was to present the techniques and knowledge on sustainable mineral exploration that have been developed within the INFACT and PACIFIC projects. The school targeted an audience of European master students, PhDs and post-doctoral researchers. A total of 40 students, including 15 from the University of Huelva, physically attended the school. An additional 13 students participated in parts of the school via video conference, since unfortunately due to travel restrictions stemming from the COVID-19 pandemic those 13 students were unable to attend in person. Videoconferencing was a last-minute adaptation made by the Winter School to allow for the participation of individuals under travel bans, quarantine, or other restrictions. Students (both physical and remote attendees) came from 13 countries. The results of the anonymous survey conducted at the end of the school reveal that the event was a success, despite the ongoing COVID-19 crisis.

Retrieving reflection arrivals from passive seismic data using Radon correlation

Since explosive and impulsive seismic sources such as dynamite, air guns, gas guns or even vibroseis can have a big impact on the environment, some companies have decided to record ambient seismic noise and use it to estimate the physical properties of the subsurface. Big challenges arise when the aim is extracting body waves from recorded passive signals, especially in the presence of strong surface waves. In passive seismic signals, such body waves are usually weak in comparison to surface waves that are much more prominent. To understand the characteristics of passive signals and the effect of natural source locations, three simple synthetic models were created. To extract body waves from simulated passive signals we propose and test a Radon-correlation method. This is a time-spatial correlation of amplitudes with a train of time-shifted Dirac delta functions through different hyperbolic paths. It is tested on a two-layer horizontal model, a three-layer model that includes a dipping layer (with and without lateral heterogeneity) and also on synthetic Marmousi model data sets. Synthetic tests show that the introduced method is able to reconstruct reflection events at the correct time-offset positions that are hidden in results obtained by the general cross-correlation method. Also, a depth migrated section shows a good match between imaged horizons and the true model. It is possible to generate off-end virtual gathers by applying the method to a linear array of receivers and to construct a velocity model by semblance velocity analysis of individually extracted gathers.

Monitoring of fields using body and surface waves reconstructed from passive seismic ambient noise

There are important economic, environmental and societal reasons for monitoring production from oil, gas and geothermal fields. Unfortunately, standard microseismic monitoring is often not useful due to low levels of microseismicity. We propose to use body and surface waves reconstructed from ambient seismic noise for such monitoring. In this work, we use seismic data recorded from a dense sensor array at the Groningen gas field in northern Holland and show how direct P-waves can be extracted from the ambient noise cross correlations and then used to monitor seismic velocity variations over time. This approach has advantages over the use of coda wave interferometry due to the ability to localise such changes in the subsurface. We show how both direct and refracted (head) P-waves as well as Rayleigh surface waves can be used for such field monitoring, with changes of ∼1% being resolved. Both fundamental and first overtone Rayleigh waves are used to localise such changes, which correspond nicely to known geology to within 100 m.

Executive summary: This document describes the structure and contents of the public website set up for PACIFIC on 29th November 2018 with the URL http://www.pacific-h2020.eu and updated in August 2020 to give more visibility to the expected impact of the project on mineral exploration in Europe, and reflect changes in the consortium. The website is based on Responsive web design (RWD), which provides an optimal viewing and interaction experience — easy reading and navigation with a minimum of resizing, panning, and scrolling — across a wide range of devices (from desktop computer monitors to mobile phones).

On the PACIFIC public website, you can find information about the project objectives and results, the concept, work plan and expected impact, together with the list of participants, external advisors and projects identified for clustering opportunities. The website also acknowledges the financial support received under the European Union’s Horizon 2020 research and innovation programme with the EU emblem as well as a specific statement. This is visible at the bottom of every webpage.

Throughout the project the PACIFIC public website will become a major tool to present the project research outcomes to a wide audience with: links to scientific peer-reviewed publications, project documentation, public deliverables and press releases available for download. On-going activities will also be regularly updated and communicated through news and events.