Unfortunately, as Mr. Oldham shows, a very different, and more
probable, interpretation may be given of these results; for all the
calculated changes are rendered uncertain by the choice of the two
stations which form the ends of the new base-line. One at least may
have been displaced by the structural movements within the epicentral
area; and, moreover, the line joining them runs nearly north and
south. As compression in this direction is to be expected, it is
probable that this line was shortened; and the assumption that its
length was unchanged would therefore lead to an apparent expansion of
all the other sides.
The calculated changes seem to favour this explanation to a great
extent. The sides joining Mopen, Rangsanobo, and Thanjinath run nearly
east and west, and are apparently lengthened by 4.9 and 3.4 feet
respectively; while, of the four sides joining these stations to
Mosingi and Mun, lying next to the north, two are nearly or quite
unchanged, and the others increased by 2.3 and 3.2 feet. Again, the
estimated increase of the Mosingi-Mun line is 4.4 feet; while the four
sides joining these stations to the next northerly group are
increased by small amounts--namely, 1.2, 2.6,-0.3, and 2.4 feet. Thus,
the apparent expansion that should have occurred in these more or less
northerly sides is lessened, or roughly compensated, probably by a
compression of the whole region in a meridianal direction.
For a similar reason, the slight general upheaval of the hills
indicated by the repeated calculations, must be regarded as doubtful,
for it depends on the assumed fixity of the station of Rangsanobo,
whereas it is more probable that it was the height of Taramun Tila
that remained unchanged. Reducing the calculated heights of all the
other stations by six feet (the assumed rise of the latter), it
follows that, on the whole, the height of the Khasi hills underwent
but little change, except at Mautherrican and Landau Modo, and the
secondary stations of Mairang and Kollong Rock, near Maonoi. The
apparent elevations of 24, 17, 11, and 15 feet at these places exceed
the probable error of the observations; and it is worthy of notice
that all four stations lie close to the edge of fault-scarps, while
Landau Modo is not far from two of the pools formed by distortion of
the surface unaccompanied by faulting.
If, then, the revised triangulation of the Khasi hills has failed to
provide absolute measures of the displacements in the epicentral area,
it has, nevertheless, proved that important movements, both horizontal
and vertical, have taken place.
Public-domain text, read in full here on John Shaqi.
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