APPLICATION OF REMOTELY SENSED DATA FOR NEOTECTONICS STUDY IN
WESTERN MONGOLIA
Tsehaie Woldai* & Javkhlanbold Dorjsuren**
*International Institute for Geoinformation Sciences & Earth Observation (ITC), Hengelosestraat 99. P.O.Box 6, 7500AA Enschede,
The Netherlands. woldai@itc.nl
** Geological Information Centre of Mongolia, Ulaan Bataar, Mongolia Javkhlanbold@ite.nl
Commission VI, Working Group V
KEY WORDS: Remote Sensing, Earthquakes, Application, Interpretation, ASTER, Landsat TM, Neotectonics, Imagery.
ABSTRACT:
Landsat TM and ASTER data were used in the neotectonics study of Western Mongolia. The latter has been one of the most seismically
active intracontinental regions of the world in this century. The occurrences of earthquakes are mostly controlled by active faults. The
relief in the area is remarkable due to its sharp contrasts and the multitude and variability of the morphological elements: high rugged
mountains, basins, and wide hilly areas composed of loose sands, gravels and boulders. In an area such as this, where the morphology of
the terrain responds to a cold, dry climate and where erosion is slow, fault ruptures cutting pediment surfaces are well preserved. Various
geomorphic features supporting recent tectonic movements were deciphered from the various remotely sensed data. These include:
strike-slip faults, fault line scarps, triangular facets, uphill facing scarps, pressure-ridges, abrupt change in topographic slope angles along
fault traces, offset drainage, truncated fan and beheaded drainage. Most of these features were examined in the field and revealed
movements that have occurred during the Holocene (past 10,000 years).
1. INTRODUCTION
Western Mongolia and its surroundings have been one of the
most seismically active intracontinental regions of the world in
this century (Fig.1). Many surface ruptures reflecting Paleogene
and recent earthquakes have been observed and attest to the
high seismic activity of this region (Baljinnyam et al., 1993;
Bayasgalan, 1995; Schlupp, 1996, Woldai & Bayasgalan, 1998).
It is a spectacular natural library for studying faults and great
earthquakes that occur in the interior of continents far from
plate boundaries. The ruptures associated with earthquake event
are well preserved due to the sparse population and the cold,
arid climate.
2. RESEARCH OBJECTIVES AND APPROACHES
Mapping of present day morphological features provide
important, though indirect clues for delineating active faults
related to neotectonics. Peculiar patterns, for example, bending
and offsetting of streams, linear ridges, pressure ridges,
beheaded streams, offset drainage, triangular facets, open rifts
and prominent scraps, and their alignments in certain directions,
can indicate recent movements. These features might sometimes
be difficult to map in the field, but could be easily deciphered
from remote sensing images, due to their advantage of polar
synoptic overview. The purpose of this paper is to describe the
results of mapping of major active faults and other neotectonic
features in the Shagryn Basin of western Mongolia (Fig.1b).
This has been achieved using Landsat TM and ASTER. The
information extracted from these datasets is validated in the
field. Other sources of information used included published
literatures, the catalogue of Mongolian earthquakes up to 2000,
a 1:300,000 scale geological map and the USGS Gtopo30
elevation map of the area. The digitally processed Landsat TM
and ASTER data proved useful in determining the structure and
drainage pattern of the area. They also proved effective in
detecting, delineating and describing the characteristics of
active faults, their orientation and direction of movement.
3. STUDY AREA
The current study area (Fig.la/b) lies between 45? 40' to 46"
40"N and 94° 00° to 95° 40°E. It is situated in the southwestern
part of Mongolia, mainly at the northern junction where the
NW-SE trending Mongolian Altay range meets the E-W
trending Gobi Altay Range in its southern junction.
Traditionally, the geographic boundary between the two Altai is
somewhat arbitrary (Woldai & Bayasgalan, 1998). The opposite
senses of active strike-slip displacement however, make it
difficult to treat the two Altays' as a tectonic continuation of one
another. The southern end of the Mongolian-Altay is taken to be
directly south of the Shargyn Tsagaan Basin (Figs.1a), where the
mountain ranges trend east west. This is a convenient boundary
because, unlike the situation in the Mongolian-Altay where right-
lateral strike-slip faulting is pervasive, left-lateral strike-slip
faulting with components of reverse faulting occurs on easterly
trending planes that bound the mountains of the Gobi-Altay.
These conjugate strike-slip faults appear to be reverse and thrust
faulting that absorbs the stress of the India-Asian collision
(Molnar and Tapponnier, 1975; Tapponnier and Molnar, 1977;
1979) with shortening rates accommodating roughly 2 mm/y
(by suggestion of Molnar).
4. ACTIVE STRUCTURES WITHIN THE SHARGYN
BASIN
The subsurface of the Shargyn Basin contains about 1000 m
thick of Meso-Cenozoic sediment (Zorin et al, 1982), and
borehole evidence shows it to be floored with Precambrian
basement granite-gneiss near the Har Tolgoin Hudag well
(Togtoh et al., 1994). The oldest basin fill comprises of Jurassic
conglomerates and sandstones overlain by Lower Cretaceous
1192
