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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X-Ray Fluorescence Spectroscopy (XRF). Amptek Inc. Bedford, MA, 2002.<www.amptek.com/xrf.html>