Evaluation of the Geophysic al Investigations for Rapid M

apping

the Maha Sarakham Rock Sa lt Formation in the Northeas

t, Thailand

Background• MahaSarakhamRockSaltFormationhasbeen

found in the twobasins. It is estimated that th e rocksalt containsmore than1 8 millionmill

ion tonesof salt (Suwanich, 1 9 9 4 )while th e annualworld saltproduction recorded for1

9 9 8 indicates that the saltwasusedat the amountof~1 8 6 million tonesperyear (Sal

2000t Institute, ). Thus theMahaSarakham mmmm mmmm mmm mm mmmmmmmmmm mm mmm mm mmm mmmmm tantmineralresources for theworl d. These ri chdepos itscancontri bute toour wel l bei ng.

Problems• At low pressure and temperature conditio

ns, the rock salt can behave as viscous flui d that can flow easily. Through time, this f

luid property of rock salt can produce com plex deformation in subsurface geology.

• When the Maha Sarakham Rock Salt is bur ied deeply, it becomes mobilized and may

flow upwards to form salt domes, deform i nto discordant bodies, lubricate and fill in

surrounding gaps, and drag adjacent strat a.

Problems• Subsurface geology correlation based on b

orehores has been found to be very difficult ! Rock salt depth found from a fewmeters

to thousandmeters from surface.• Saline soil with white granular substances

of salt on the ground have been exposed du ring the summer time or all year round in se

veral places in the two basins. Land loss du e to salt affect soil has been increased from

5.6% (1984) to 17% (1999)!

What need todone

• An increased abundance of saline soil and sa line water have been found and documented

, a thorough study on subsurface geology is needed prior to exploiting the rock salt and d

evelopment a plan for land use to stop harmf ul effects of the rock salt in ecosystem.

• The rock salt depth needs to be mapped for t he entire basins to allow relocation the lands

that are suitable for agricultural activities an d salt production.

What need todone

• Apply in expensive and effe ctive techniques (i.e., geop

hysical investigations) for r apid determination of subs

urface geology of the rock s alt formation.

Objectives of study

• Conduct three geophysical expe riments including

• Seismic refraction and reflect ion

• Gravity and magnetic• Resistivity and electromagnetic

Results and discussions

• Seismic refraction and reflecti on experiments

• Gravity and magnetic experiments• Resistivity and electromagneti

c experiments

Conclusions• Seismic refraction or reflection

with a single fold can be used t o detect the rock salt.

• Gravity survey alone fails to de tect the rock salt layers becau

se of insufficient in the density between rock salt and clayston

e.

Conclusions• Resistivity and electromagnetic surveys ca

n be used to detect the interface between rock salt and saline water, although the re sults are not conclusive since the measura

ble bulk resistivity or conductivity did not seem to correlate with the distinct rock sal

t and the saline water interface. Further st udies are needed to derive a definitive con

clusion!

Conclusions

• Nomagnetic anomaly can be resolved from the rock s -alt layer because of low lev

el contrast in magnetic sus ceptibility of the rock salt r

elative to the background. Any question!