identifying tsunami deposits in the field using pxrf: lhok...
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Identifying Tsunami Deposits inthe Field Using PXRF: Lhok Ngaand Banda Aceh, Indonesia
Peter MeleneyWhitman College
Dr. Susan E.H. SakimotoUniversity of Notre Dame
Interdisciplinary Studies in Tsunami Impacts and MitigationUniversity of Notre Dame, Department of Civil Engineering and Geological Sciences
Objective:To increase the accuracy oftsunami hazard mapping throughrapid field identification of tsunamideposits using a Portable X-RayFluorescence (PXRF) spectrometer.
Approach Identify the geochemical signs of
tsunami deposition Determine proper techniques for PXRF
analysis Use the PXRF to distinguish tsunami
deposits from other types of near-shoresedimentation
Why is this ResearchImportant?
Recurrence intervaldetermines hazard Detailed history leads
to better predictions Guides codes and
preparations
Used for many typesof geologicalphenomena
http://i.pbase.com/u13/minoltaman/large/38394818.horribledevastation.jpg
Problems with CurrentRecurrence Determination
Ways to findrecurrence: Historical record
Not statisticallysignificant
Tsunamiite beds Hard to recognize Only left by >5m
waves
http://upload.wikimedia.org/wikipedia/commons/thumb/a/a5/Tsunami_by_hokusai_19th_century.jpg/800px-Tsunami_by_hokusai_19th_century.jpg
Problems with CurrentRecurrence Determination
Ways to findrecurrence: Historical record
Not statisticallysignificant
Tsunamiite beds Hard to recognize Only left by >5m
waves
http:http://geoscape.nrcan.gc.ca/nanaimo/images/tsunami hazard e.jpg
Why are Tsunami Depositshard to Identify in the Field?
Current practices Based entirely on
physical evidence Chemical results take
several days toprocess
Similar to storm surgedeposits
Not used Field results
geochemical signature
Photo courtesy Tamara Carley
Sediment Source Tsunamis involve
the entire watercolumn Sediment from
ocean bottom
Storm surgesinvolve top fewmeters Near-shore
sediment only
http://www.ga.gov.au/image_cache/GA9426.gifGingele et. al. 2001
Sediment Source
Banda Aceh Illite is verypotassium rich Ocean clay:
2.1-3.0 wt% K Terrestrial soil:
~0.02 wt% K
http://www.ga.gov.au/image_cache/GA9426.gifGingele et. al. 2001
Sediment Source
Banda Aceh Illite is verypotassium rich Ocean clay:
2.1-3.0 wt% K Terrestrial soil:
~0.02 wt% K
http://www.ga.gov.au/image_cache/GA9426.gifGingele et. al. 2001
Hypothesis: The clay fraction of tsunami deposits will havea significantly higher concentration of potassium thansurrounding sediments
Where to Find Tsunami Clay
http://whyfiles.org/shorties/168tsunami_warn/images/tsunami.jpgPhoto courtesy Tamara Carley
How can the PXRF Help? In-situ elemental
concentrations K in field: precise
to within 16 wt%
Bombards samplewith X-rays Elements have
characteristic X-ray spectra
http://www.amptek.com/pdf/xrf.pdf
Methods
Photo courtesy of Tamara Carley
Store for laboratory analysis (XRD, ICP-MS)
Re-analyze using the PXRF in the field
Wash through a seive to isolate the silt and clay sized fraction
Store for laboratory analysis (XRD, ICP-MS)
Re-analyze sample in the field using PXRF
Split sample into two equal portions of at least 25 g each
Collect 50 g of sample
In-situ analysis with PXRF
Expected Results
Washed and sieved samples will show betterresults Potassium is diagnostic
Ocean clay detectable at very low concentrations ~5 wt%
Conclusions Tsunamis pose a threat to coastal
communities around the world Many tsunami hazard models are
based on insufficient data The PXRF provides an important
tool for evaluating sediments inthe field Speed of test allows for sample
screening and selection
AcknowledgementsMade possible be a grant from theNational Sicence Foundation (EEC 05-52432)
Susan E.H. SakimotoTamara CarleyUniversity of Notre Dame
http://www.chemx.org/National%20Science%20Foundation%20(png)%20.pnghttp://www.nextgnetworks.net/i/NDUlogo.jpg
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