INTERPRETATION OF SATELLITE DATA RELATED TO NEOTECTONIC ACTIVITIES CONNECTED WITH
EARTHQUAKES IN WESTERN MONGOLIA
Dr. TSEHAIE WOLDAI
International Institute for Aerospace Survey & Earth Sciences (ITC), Enschede, The Netherlands
Mr. A. BAYASGALAN
Informatics Centre, Mongolian Academy of Sciences, Ulaanbaatar, Mongolia
ISPRS Commission VII, Working Group 7
KEY WORDS: remote sensing, neotectonics, seismic hazard, active faults, Holocene, Mongolian-Altay, Gobi-Altay.
ABSTRACT
Westem Mongolia has been one of the most seismically active intracontinental regions of the world in this century. The occurrences of
] earthquakes in this region are mostly controlled by active faults. The relief of the area as seen from Landsat TM, SPOT and the Russian
KOSMOS stereo satellite image prints, is remarkable due to its sharp contrasts and the multitude and variability of the morphoiogical
elements: high rock ridges, flat downwarped stony plains, high mountain piedmonts, basins, and wide hilly areas composed of loose
sands. In an area such as this, where the morphology of the terrain responds to a cold, dry climate and where erosion is slow, fault
g to ruptures cutting pediment surfaces are well preserved. Various geomorphic features supporting recent tectonic movements were
onal deciphered from the various remotely sensed data. These include: strike-slip faults, fault scarps, fault line scarps, triangular facets, uphill
facing scarps, linear fault valleys, fault angle valleys (halfgraben), shutter-ridges, abrupt change in topographic slope angles along fault
lote | traces, pressure ridges, sagponds, offset drainage, truncated fan and behaded drainage. Most of these features were examined in the field
and revealed Holocene neotectonic activity.
786-
1. INTRODUCTION using remotely sensed data is feasible. The synoptic view evident
in this kind of data in Mongolia facilitates the synthesis of regional
Earthquakes are the expression of the continuing evolution of the geological and structural features, such as the various neotectonic
[ earth planet and its surface. They are caused by the rupture and structural zones and is effective in detecting, delineating and
sudden movement of rocks that have been strained beyond their
elastic limits. Most of the earthquakes are controlled by active
faults or are caused by the reactivation of existing faults, as they
provide the easiest channels of release of strain.
Seismologists distinguish between the active faults and
neotectonics, calling active those which exhibit present-day
activity and, neotectonic those which have been active in the
geological recent times. Neotectonic or active faults as described
in this paper however, relate to those along which movements
have occurred in the Holocene (past 11,000 years). Within the
present state of the art, active tectonic studies in area such as
western Mongolia (Fig.1 ), on a semi-detailed and detailed scale
{Maur :
sa. "es
(3 > AM v #5 =
777) 1000-1500a
[7 -
1500-2000n
[7] 2000-3000
—
~~ Int. boundary
Figure 1. Location map of the study area.
describing the character of active faults and their neotectonic
implications.
Very limited publications are available on the tectonism of
western Mongolia. Much of what is known is derived from the
satellite imagery based interpretations of Tapponnier and Molnar
(1977), and on major earthquakes and active fault scarps from the
work of Baljinnyam et al. (1993). The main monograph published
in Russian and related to the present work is the book of Khil ko
et al. (1985).
This study aims to examine the complex structures present within
western Mongolia and understand some of the neotectonic
TTT IAN processes and implications using remotely sensed dataset
2 -— = Da; or . . a
NS 9 LS E. cc available of the region, fieldwork and the geological data of the
at = Az Bi : area collected in the last 30-40 years.
2. DATASETS USED
Landsat Thematic Mapper (TM) image (path 134, row 29 and
acquired on 8 February, 1989), SPOT data (K-244, J-247 from 20
April 1992 and K-245, J-259 from 3 April, 1992) and Russian
KOSMOS data of the Mongolian-Gobi-Altai ranges were
interpreted to show the behavior of main faults and joints in the
area and to determine the relationship between the basement
rocks, forming mountains and meso-Cenozoic terrigeneous rocks
filling the intermontane basins. The image acquisition date of the
Russian KOSMOS date is not known. The most Russian satellites
of KOSMOS type however have an orbiting altitude of 220-250
= nee km. Black and white stereo contact prints of size 18 by 18 cm and
7 river sus es having a scale of approximately 1:1,000,000 was therefore used.
The remotely sensed data used were quite useful in determining
the structural features and drainage pattern of the area. Many
Intemational Archives of Photogrammetry and Remote Sensing. Vol. XXXII, Part 7, Budapest, 1998 615
