24 March, 2010 (16:00 GMT), 5 Merrion Square, Dublin 2.
Speaker: Dr Bill Fry, GNS, New Zealand.
Title: Passive seismic imaging of an earthquake prone sedimentary basin.
Abstract:
We passively image shear-wave velocity structure in an area of dense urbanization. Wellington, the capital of New Zealand is a densely populated urban area located at the boundary of the convergent Australian and Pacific plates. It is prone to the effects of both large strike-slip and large subduction earthquakes. The city lies on the edge of a funnel shaped basin and is underlain by the strike-slip Wellington Fault. The fault has average single event displacements of approximately 5 metres for surface-rupturing events. These events represent a significant seismic hazard. In order to accurately model wave propagation and basin resonance resulting from earthquake scenarios derived from geological mapping and calculations of synthetic seismicity, we must accurately know the basin geometry and velocity structure. Geotechnical data in the basin is sparse and insufficient to provide a full 3D basin model. The dense human development precludes the use of active source seismic imaging. We therefore apply noise-based, passive seismic imaging to define velocity structure and basin geometry. We begin by implementing an interferometry approach to isolate the surfacewave compenent of the interstation Green’s Function between a pair of stations. Due to the contaminating presence of anthropogenic sources proximal to stations, only data with shortterm power spectra that are below the site’s long-term average are correlated. Dispersion observations measured from the stacked correlation functions are inverted with a non-linear algorithm to find a suite of likely Vs profiles. To image shallower velocities, we also apply an array-based spatial autocorrelation technique (SPAC). In this method, we find the azimuthally averaged coherency between recordings at a triangular array of seismometers. The
coherency is then directly inverted for shallow velocity structure with a linear perturbation approach. By using both spatial autocorrelation (SPAC) and 2-station interferometry approaches, we map shear wave velocity on scales ranging from metres to a few hundred metres and provide a detailed basin velocity model for subsequent efforts focused on numerical modelling of the wavefields for plausible earthquake scenarios.
Leave a Comment
Last Updated: 22nd March 2016 by Anna
2010-03-24 – SEMINAR by Dr. Bill Fry: Passive seismic imaging of an earthquake prone sedimentary basin
24 March, 2010 (16:00 GMT), 5 Merrion Square, Dublin 2.
Speaker: Dr Bill Fry, GNS, New Zealand.
Title: Passive seismic imaging of an earthquake prone sedimentary basin.
Abstract:
We passively image shear-wave velocity structure in an area of dense urbanization. Wellington, the capital of New Zealand is a densely populated urban area located at the boundary of the convergent Australian and Pacific plates. It is prone to the effects of both large strike-slip and large subduction earthquakes. The city lies on the edge of a funnel shaped basin and is underlain by the strike-slip Wellington Fault. The fault has average single event displacements of approximately 5 metres for surface-rupturing events. These events represent a significant seismic hazard. In order to accurately model wave propagation and basin resonance resulting from earthquake scenarios derived from geological mapping and calculations of synthetic seismicity, we must accurately know the basin geometry and velocity structure. Geotechnical data in the basin is sparse and insufficient to provide a full 3D basin model. The dense human development precludes the use of active source seismic imaging. We therefore apply noise-based, passive seismic imaging to define velocity structure and basin geometry. We begin by implementing an interferometry approach to isolate the surfacewave compenent of the interstation Green’s Function between a pair of stations. Due to the contaminating presence of anthropogenic sources proximal to stations, only data with shortterm power spectra that are below the site’s long-term average are correlated. Dispersion observations measured from the stacked correlation functions are inverted with a non-linear algorithm to find a suite of likely Vs profiles. To image shallower velocities, we also apply an array-based spatial autocorrelation technique (SPAC). In this method, we find the azimuthally averaged coherency between recordings at a triangular array of seismometers. The
coherency is then directly inverted for shallow velocity structure with a linear perturbation approach. By using both spatial autocorrelation (SPAC) and 2-station interferometry approaches, we map shear wave velocity on scales ranging from metres to a few hundred metres and provide a detailed basin velocity model for subsequent efforts focused on numerical modelling of the wavefields for plausible earthquake scenarios.
Category: Geophysics Section News & Events
Big thank you to @MartinaPQuinn of @helloalicepr for moderating the discussion, and of course to our panel @NeasaMcG @CormacORafferty and @laoneill111
@CormacORafferty "to cut yourself off from fundamental research means you could miss out on some of the biggest ideas"
@laoneill "it's our job as researchers to keep reminding governments how important basic research is" "For Dev basic research being carried out in Ireland was a badge of pride"
@NeasaMcG Schrödinger's work in causality was not well received by the religious authorities at the time At the same time DIAS did have Catholic priests working on research projects in the early days, so there was not the conflict you might think between science and religion
@laoneill111 Schrödinger was very popular in social circles in Dublin, a bit of a renaissance man
@CormacORafferty Schrödinger was gifted at explaining difficult concepts
@CormacORafferty on how unsuccessful work, in Schrödinger's case, unified field theory, is just as important part of science. And no one has managed to crack it yet! And not forgetting the cat
@laoneill111 how Schrödinger's book inspired scientists to change fields and result in the finding of the double helix.
@NeasaMcG explaining how DIAS came about and how Schrödinger was attracted to Ireland #DIASdiscovers
Panel Discussion getting underway! @laoneill111 @CormacORafferty @NeasaMcG @MartinaPQuinn
We're half way through the documentary... Join us for the rest and the fascinating discussion to follow DM for link
@Stella15882 @NeasaMcG @HistFest @lukeoneil47 @CormacORafferty @MartinaPQuinn Stella, send me an email. I'll get a link to you communications@dias.ie
Starting in just over an hour we have limited tickets left for tonights broadcast and panel discussion. Get your free ticket now twitter.com/DIAS_Dublin/st…
Culture Night 2020 Booking Links! - Virtual Tour of DIAS Dunsink Observatory: eventbrite.ie/e/118043576515 - Earthquakes and other Geohazards: eventbrite.ie/e/earthquakes-… - Taifeadaí Cartlainne ó Scoil an Léinn Cheiltigh: eventbrite.ie/e/taifeadai-ca… Join us from 5pm! #CultureNight2020
@dias_geophysics have developed something special for @galway2020 in collaboration with composer David Stalling. It is an audio-visual composition “Palace of Ships,” based on sounds, images and seismic data from DIAS’ @SEA_SEIS Expeditions. More: dias.ie/2020/09/14/dia…
Meet some of our panelists for tomorrows discussion on the impact and legacy of the work carried out by Erwin Schroedinger during his time in Ireland as our first Director of Theoretical Physics Grab a free ticket here: eventbrite.ie/e/115984908985