Open software

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Access to seismic full wavefield modelling tools (WP23)

Description

VolcSeisSimu: Forward modelling of seismic waves in 2D & 3D heterogeneous media using the Elastic Lattice Method

The infrastructure comprises a software tool (ELM) for the numerical modelling of seismic wave propagation in highly heterogeneous media (including media with fractures). The tool kit also comprises starter heterogeneous volcano models. Whilst full wavefield simulators are becoming more common, a unique aspect of this tool is its ability to handle media with discrete fractures of arbitrary scale, in addition to intrinsic geological heterogeneity.

The Elastic Lattice Method (ELM) is a discrete particle numerical method for simulating seismic wave propagation through complex media in the presence of topography. The model structure consists of particles arranged on a cubic lattice which interact through a central force term and bond-bending force. Particle disturbances are propagated through space by numerically solving their equation of motion. A description of the code, examples, and bench marking against finite difference codes can be found in references [1-6]. The ELM code has both 2D and 3D implementations.

Potential application in volcano observatories

The aim of volcano monitoring is to understand physical processes within a volcano and ultimately help in forecasting potential hazards. One of the primary interests in volcano-seismology is determining volcanic seismic sources, but the generation and propagation of seismic waves throughout volcanic regions is a complex and nonlinear phenomenon controlled by the interaction of many processes. Because volcanoes are highly mechanically heterogeneous they significantly distort seismic wave propagation and hence the source ‘fingerprint’ in seismograms is often hidden by ‘path effects’ created when the wave propagates from to the source to the seismic receiver. Using the VolcSeisSimu tool researchers or monitoring scientists can determine these propagation path effects for arbitrarily heterogeneous models and ‘deconvolve’ them from observed seismograms to better understand and constrain volcano source models. Source inversion is a highly specialised and time consuming research area, but is critical to a better understanding of volcano seismograms in terms of source processes. This scheme offers an alternative 3D method for modelling wave propagation in the presence of strong topography and subsurface heterogeneity, and the flexibility of the method allows for a wide range of possible source mechanisms with no restriction on source geometric shape or on the distribution and degree of elastic heterogeneity.

Access

The manual with information about how to compile and run the code is available here:

https://git.dias.ie/graphiit/DIASGEO/wikis/home

The seismic simulation codes are available to download here:

https://git.dias.ie/graphiit/DIASGEO

References

[1] O'Brien, Gareth S., Bean, Christopher J. (2004), A 3D discrete numerical elastic lattice method for seismic wave propagation in heterogeneous media with topography, Geophys. Res. Lett., Vol. 31, No. 14, L14608 doi:10.1029/2004GL020069.

[2] O'Brien, G. S., Bean, C. J. (2004), A discrete numerical method for modeling volcanic earthquake source mechanisms, J. Geophys. Res., Vol. 109, No. B9, B09301 doi:10.1029/2004JB003023.

[3] O'Brien, G. S. (2008), Discrete visco-elastic lattice methods for seismic wave propagation, Geophys. Res. Lett., 35, L02302, doi:10.1029/2007GL032214.

[4] O'Brien G.S., Bean C.J. and Tapamo H. (2009), Dispersion analysis and computational efficiency of Elastic Lattice methods for seismic wave propagation, Computers & Geosciences, Vol. 35, 1768-1775. doi:10.1016/j.cageo.2008.12.004.

[5] O'Brien, G. S. and C.J. Bean (2011), An irregular lattice method for elastic wave propagation, Geophysical Journal International, doi:10.1111/j.1365-246X.2011.05229.x.

[6] O'Brien, G.S., T. Nissen-Meyer and C.J. Bean (2012), A Lattice Boltzmann method for elastic wave propogation in a Poisson solid, Bulletin of the Seismological Soceity of America, VOLUME 103, No. 3, Pages 1224-1234, doi:10.1785/0120110191.


RETREAT - a REal-time TREmor Analysis Tool (WP9)

Description

RETREAT is a REal-time TREmor Analysis Tool written in python, making use of the obspy framework. It performs frequency-wavenumber (f-k) analysis on realtime (or optionally archive) seismic array data to calculate the back azimuth and slowness values in a given time window, with the aim of aiding in the location and analysis of volcanic tremor signals.

Access

Full documentation on how to download, install and run the software is available here:

https://git.dias.ie/paddy/retreat

References

Eibl, Eva P. S., Bean, C.J., Vogfjörd, K.S., Ying, Y., Lokmer, I., Möllhoff, M., O’Brien, G.S., & Pálsson, F. (2017a). Tremor-rich shallow dyke formation followed by silent magma flow at Bárðarbunga in Iceland. Nature Geoscience volume 10, pages 299–304, doi:10.1038/ngeo2906

Eibl, E. P. S., Bean, C. J., Jónsdóttir, I., Höskuldsson, A., Thordarson, T., Coppola, D., Witt, T., and Walter, T. R. (2017b), Multiple coincident eruptive seismic tremor sources during the 2014–2015 eruption at Holuhraun, Iceland, J. Geophys. Res. Solid Earth, 122, 2972– 2987, doi:10.1002/2016JB013892.