19 September 2014 – Seminar

When: 16:00 on Friday, 19 September 2014
Where: DIAS, Geophysics Section, 5 Merrion Square, Dublin 2, (library)

Speaker: Nicola Piana Agostinetti (DIAS)
Title: Trans-dimensional Monte Carlo sampling for structure decoupling: an application to geophysical inverse problems

Abstract:

Trans-dimensional (trans-D) algorithms have been recently introduced to the earth sciences to solve inverse problems without having to impose a fixed spatial structure to the model parametrization (e.g. a fixed number of layers in a 1D structure). Trans-dimensional algorithms can be easily used for joint inversion of different data-set using a “Hierarchical Bayes” approach. However, some difficulties arise if the two observables display very different resolving power. In this case, the structure of the target solution might be twisted toward one observable, introducing non resolved (i.e. over-complex) structure for the other investigated parameters. In this study, we develop a trans-D algorithm for joint inversion of two different data-sets to reconstruct the 1D structure of two different physical parameters. The “parsimony” of the trans-D algorithm produces common discontinuities (a “coupled” structure) for portions of the 1D profile where the two observables displays similar resolving power, while the two reconstructed 1D structures will be different (i.e. the two structure are “decoupled”) where the two observables have different resolving power.

A. Schaeffer (r) with his PhD advisor S. Lebedev

Andrew Schaeffer of the Geophysics Section (School of Cosmic Physics) is the Inaugural Winner of the Graduate Research Award, presented by the Study of the Earth’s Deep Interior Focus Group (SEDI), American Geophysical Union.

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When: 4pm on Monday, September 1st, 2014
Where: DIAS Merrion Square Library

Speaker: Jim Craven, Geological Survey, Ottawa

Title: The Aquistore Project: Baseline Seismic and EM Studies of Commercial-Scale CO2 Storage in a Saline Aquifer in Saskatchewan, Canada
Description: The Aquistore project is a large-scale carbon dioxide (CO₂) capture and sequestration initiative, taking place in southern Saskatchewan, Canada.  Emissions of CO₂ generated from SaskPower’s nearby Boundary Dam Power Station are to be captured and injected, in liquid form, deep into stable sedimentary packages of the Williston Basin for long-term storage and use in enhanced oil and gas recovery. The overall aim of the project is to reduce greenhouse gas emissions coming from a fixed source of CO₂ discharge, while demonstrating the effectiveness of using geological formations as a sequestration reservoir. 

The Aquistore reservoir will be the Cambro-Ordovician aquifer system of the Deadwood and Winnipeg Formations of the Williston basin which forms part of the Western Canada Sedimentary Basin. The primary target is at 3400 m depth, which is deep in comparison to other CO₂ site studies. The reservoir at Ketzin is at 635-650 m depth, at Hontomín it is at 1350-1460 m, and at Kevin Dome it is at 3000 m. The challenging depth of investigation has led to the development of a number of novel data acquisition technologies, particularly those deployed within a nearby observation well drilled to similar depths as the injection well. This talk will review baseline surface and downhole seismic and (controlled and natural source) EM studies conducted prior to injection expected in late October or November 2014.

When: 4pm on Friday, August 1st, 2014
Where: DIAS Merrion Square Library

Title: Mountain building and mantle dynamics: a journey through the Tethyan belt
Description: The style of mantle convection beneath large oceanic plates is rather well established. On the other hand, we still have a loose grasp of what happen beneath continental plate, especially beneath mobile and convergent margins, where we expect to have vigorous convection. Here, I present some considerations about the style and evolution of mantle convection beneath convergent/collisional zones as constrained by geological – seismological data and modelling. I will consider the Alpine-Tethyan belt as a case study, exploring the idea that the style of mountain building can be used as a proxy to reconstruct mantle dynamics. The Tertiary evolution of the Tethyan belt indeed offers a unique opportunity to discuss about mountain building and mantle dynamics, as it include region such as the Mediterranean, where collision is still in its incipient stage producing Apennines style orogen, to the Himalayan-Tibetan belt, where collisional process reaches its extreme consequence. We classified those two belts as end members of a wide range of orogen. On one side, the of “slab pull” orogen, where subduction is mainly confined to the upper mantle, and rollback trench motion lead to moderately thick crustal stacks and reduced topographic signal, such as in the Mediterranean. On the other side, the “slab suction” orogen, where whole-mantle convection cells (“conveyor belts”) lead to the more extreme expressions of orogeny, such as the largely thickened crust and high plateaus of present-day Tibet. For the slab suction type, deep mantle convection produces the unique conditions to drag plates toward each other, irrespective of their nature and other boundary conditions. Based on mantle circulation modeling and tectonic reconstructions, we surmise that the forces necessary to sustain slab-suction mountain building in those orogens derive, after transient slab ponding, from the mantle drag induced upon slab penetration into the lower mantle, and from an associated surge of mantle upwelling beneath Africa. This surge of mantle convection drags plates against each other, generating the necessary compressional forces to create and sustain these two orogenic belts. If this “bottom-up” tectonic model is correct, the geological records of orogeny cycle and of the topographic evolution along mobile belt can be used to decipher time-dependent mantle convection. Our main conclusion is that beneath the Tethyan belt we should imagine a multi-scale style of convection operating at different time and length scale, with a small scale convection style in the upper most part of the upper mantle embedded within a larger/slower and intermittent large scale whole mantle convection.

29^th April 2014 – Magnitude 0.8 event recorded in Donegal

On29^th April 2014 at 04:02:01 UTC an earthquake of magnitude ML0.8 occurred in Donegal,location 55.16N, 7.43W. This event was recorded at Irish National Seismic Network (INSN) station in Donegal (IDGL), SIM Crust temporary stations in DOnegal and by neighbouring stations in Northern Ireland. There are no felt reports at this time.

This is a region of known seismicity in Ireland and the location and magnitude of this event are of an order that would be expected for this region.

If you felt this event please fill out our questionnaire.

Earthquake of coast Northern Chile 01-04-14

A major M8.2 earthquake occurred off the northern coast of Chile on 1st April 2014 at 23:46 UTC (18:46 local time). This earthquake occurred in a region of historic seismic quiescence. A number of aftershocks have been recorded. A tsunami alert was issued for the Pacific region.

This earthquake occurred in a region already know as a quiescent seismic gap zone, which has had no strong seismic activity for over 100 years.

The first arrival at INSN was recorder at the VAL (Valentia) seismic station at 23:59:39 UTC.

Below is as an image of the seismic traces of the the main event  recorded on the stations of INSN.

18th March 2014 – Magnitude 2.6 event recorded off Wexford coast

On 18th March 2014 at 20:45:15 UTC an earthquake of magnitude ML2.6 occured off the east Wexford coast, location 52.36N, 6.20W. This event was felt in the Wexford area and was recorded at Irish National Seismic Network (INSN) stations. See seismogram below.

This is a region of known seismicity in Ireland and the location and magnitude of this event are of an order that would be expected for this region.

If you felt this event please fill out our questionnaire.

Geological Survey of Ireland about this earthquake.

24 March 2014 – Seminar

Details

When: 16:00 on Monday, 24 March 2014
Where: DIAS, Geophysics Section, 5 Merrion Square, Dublin 2, (library)

Speaker: Dr. Stephan Thiel (University of Adelaide)
Title: MT Down Under: From lithospheric-scale studies to geothermal applications

Abstract:

Australia is mainly characterized by Archean to Proterozoic lithosphere with vast mineral potential. Due to extended periods of tectonic inactivity and erosion, the regolith cover proves to be a major challenge to unravel the tectonic history of its terranes. This talk will highlight some examples of the use of MT to understand the large-scale tectonic architecture of the subcontinent. As a side product, the sedimentary cover provides a heat blanket over highly radiogenic granites in parts of the Australian continent, making Australia one of the most actively engineered geothermal prospects. The EGS targets differ significantly in their electromagnetic responses to conventional hydrothermal systems, yet MT proves a useful tool to image temporal variations due to geothermal fracking experiments.