Anatomy of a lava dome using muon radiography and electrical resistivity tomography Jean-François...

Anatomy of a lava dome using muon Anatomy of a lava dome using muon radiography and electrical resistivity radiography and electrical resistivity

tomographytomography

http://www.tomuvol.fr/

Jean-François LÉNAT on behalf of the TOMUVOL Collaboration

Laboratoire Magmas et Volcans, Laboratoire de Physique Corpusculaire, Laboratoire Magmas et Volcans, Laboratoire de Physique Corpusculaire, Clermont-Ferrand, Clermont-Ferrand, FranceFranceInstitut de Physique NucléaireInstitut de Physique Nucléaire de Lyon, France de Lyon, France

Origin-nature of the muons

Primary cosmic rays striking the atmospheric atoms and molecules

High-energy collisions new secondary particles are produced, among them muons (unitary negative electric charge, 207 times the mass of an electron)

and anti-muons.

About 10000 muons/minute per square meter at the surface of the Earth

Intro

From Tang et al., Phys. Rev. D74, 053007 (2006)

Energy spectrum of muons obtained from a compilation of

experimental data.

Muons arriving in the horizontal direction have a higher intensity at energies above a few 100 GeV

Because muons become more penetrative as their energy increases, near horizontal muons can be used for radiographic scanning

They can penetrate into the earth if their initial energy is sufficiently high

Flux reasonably high to keep detectors to a reasonable size for

geological applications

Intro

Intro

At the detector location, an object (e.g. a volcano) is illuminated by muons from all the directions

The opacity of the object is determined by comparing the flux crossing the object and a modeled or measured incident flux in open sky conditions.

The attenuation of the flux of muons depends on the density and size of an object along the muon trajectories

copyright by Tom Tam

Intro

If the shape of the object is known (e.g. DEM for a volcano), the average density along the muons path can be determined (radiography).

Tanaka et al., 2007

With acquisitions from different locations 3D reconstruction of density distribution (tomography).

Pioneer studies in muons radiography by :

• Alvarez et al.,1970, Chephren pyramid• Nagamine et al. 1995, Tanaka et al. 2001, Volcanoes• Borozdin et al. 2003 muon scattering radiography to detect uranium/plutonium contraband in trucks• Jenneson, 2004, Large vessel imaging

and ongoing projects in different areas:

• Volcanoes• Faults• Tunnels• Minerals deposits•…

Intro

TOMUVOL presentation

TOMUVOL (Tomographie muonique des volcans = volcano muons tomography) project started in 2010.

A collaboration between particle physicists and volcanologists from Clermont-Ferrand and Lyon (France)

Detectors derived from equipments developed for high energy physics and cosmic particles studies.

TOMUVOL presentation

The aim of TOMUVOL is to :

• Develop muon tomography of volcanoes

• Develop joint interpretations of muons and other geophysical data (gravity, electrical resistivity, …)

• Develop portable muons stations to study and monitor active volcanoes

Ongoing experiment on Puy de DômePuy de Dôme presentation

A 11 ka old trachyte dome in a young volcanic chain (the Chaine des Puys) 10 km to the West of the city of

Clermont-Ferrand (France)

The dome is about 400 m high and 1.8 km wide at its base

Interpreted as a composite dome by geologists

Photo © Daniel Massacrier Ville de Clermont-Ferrand

Puy de Dôme presentation

The Puy de Dôme has been selected as an experimental site for the Tomuvol project for:

• Proximity with the labs in Clermont-Ferrand• Good accessibility• Possibility to install the experimental equipments in existing shelters with electric power

In addition to the muon data, the following geophysical data are (or will be) available :

• 2D electrical resistivity profiles• High resolution gravity map

Muons experiment at Puy de Dôme

Milestones 2011:Jan. - July: Muon detector at Grotte TaillerieMay: Electrical resistivity measurement Dec: Muon detector at Col de Ceyssat

Milestones 2011:Jan. - July: Muon detector at Grotte TaillerieMay: Electrical resistivity measurement Dec: Muon detector at Col de Ceyssat

Col de CeyssatCol de Ceyssat(1074 m)

107 deg

Grotte TaillerieGrotte Taillerie(867 m)(867 m)

2 km

1.2 km

Puy de DômePuy de Dôme(1465 m)

From a Lidar survey in March 2011. Accuracy better than 10 cm, 0.5 m grid size

High resolution Digital Elevation Model

Puy de Dôme

Taillerie

Col de Ceyssat

The detectors (CALICE GRPC’s)


Glass Resistive Plate Chamber

Gas: 93% forane, 5% isobutane, 2% SF6; 1 l/hPCB :Printed Circuit Boards

9142 readout channels per m2

HV~ 7.5kV

insulation

glassgraphite

PCB

copper plates 1cm2 Glass Resistive Plate Chamber

gasm

uon1 mm

A charged particle ionizes the gas high electric field amplifies this ionization by producing charge cascades, which in turn induce charge signals on the copper plates


The muons telescope is composed of 3 planes of GRPC.

The electronic part provides the location of the impacts (1 cm2 pixels).

This allows to reconstruct the muons trajectories.


Positioning of the device by GPS and land surveying accuracy better than 5 mm

Remote detector control and data transfer through a WIFI link

Alignment of the planes checked by minimizing the sum of the individual-track 2s against variations in the alignment parameters.

Simulated event rates for a density of 1.6 g/cm3

Path length of the atmospheric muons across the Puy de Dôme volcano in the direction of the detector

indicates that the interior of Puy de Dôme is accessible for muon imaging with an 1 m2 large detector


Experiments in different phases:

• Phase 1. January to April 2011 : two 1m2 chambers + one 1/6 m2 chamber, telescope extension: ~50cm • Phase 2. three more weeks : three 1m2 chambers, telescope extension: ~50cm • Phase 3. until July 2011 : two 1m2 chambers + one 0.16m2 chamber, telescope extension: 1m

x

y

z

O

Track reconstruction Clusterise the coincident (0.4 µs) hits in the

three chambers Analytically minimise χ2 w.r.t. 4 track

parameters using the 3 cluster barycentres

Position resolution : 0.4 cm; Angular resolution : better than 0.5° in both and during the first two phases. Angular resolution improved by about a factor 2 for the 1 m-long setups (phase 3).



21 Jan – 6 April 2011 (65.9 days)(0.16 m2, 0.5 m telescope)

Tomuvol Preliminary

12 May- 1 July 2011 (46 days)(0.16 m2, 1 m telescope)

Tomuvol Preliminary

14 April- 12May 2011 (18 days)(1 m2, 1 m telescope)

Tomuvol Preliminary

Datasets (muon shadows) currently analyzed to derive average density along the muons path across the dome

Resistivity experiment at Puy de Dôme

2 D Electrical Resistivity Tomography carried out with a multi-electrodes (64) equipment (ABEM)

A 2205 m long south-north profile with 35 m electrode spacing

More detailed south-north and west-east profiles in the summit area (electrode spacing 5 m)

Combination of Wenner a and Schlumberger soundings to ensure good signal and good data coverage


Preliminary resistivity model along a south-north profile, showing the

heterogeneous internal structure of the composite lava dome


Preliminary geological interpretation of the resistivity model along a south-north profile.


A complete interpretation of the internal structure of the dome will be carried out using :

• Two muon datasets acquired from different points of view (one acquired in 2011 and the second one starting in December 2011)

• Two long south-north (made in 2011) and west-east (to be carried out in 2012) resistivity profiles

• A high resolution gravity survey (to be carried out in 2012)

This experiment aims to :

(1) Develop the study of volcanoes using muon techniques

(2) To improve the study of the interior of volcanoes using joint interpretation of several types of geophysical data

Anatomy of a lava dome using muon radiography and electrical resistivity tomography Jean-François...

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