Journal of Geological Society of India (Online archive from Vol 1 to Vol 78)

Peter Molnar ¹

Affiliations
1 Department of Earth, Atmospheric and Planetary Sciences Massachusette Institute of Technology Cambridge, M.A., US

Abstract

No Abstract.

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Peter Molnar ¹

Affiliations
1 Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology Cambridge, Massachusetts 02139, IN

Abstract

The great 1897 Assam earthquake probably was associated with underthrusting of the Indian subcontinent beneath the Shillong Plateau, and as such it absorbed part of India's convergence with the Himalaya. Seeber and Armbruster (1981) concluded that slip occurred on a fault that extended north beneath the Himalaya and south beneath much of what is now Bangladesh and that the east-west dimension of the rupture was 550 km. A reassessment of the information given by Oldham (1899) leads me to favor Oldham's inference that the length of the rupture was only about 200 km. The southern edge of the rupture was more likely at the southern edge of the Shillong Plateau than south of it. The possibility that the rupture extended beneath the Himalaya seems to be permissible but not provable from Oldham's observations. Thus, it would be unwise to assume that the 1897 earthquake released the strain that had accumulated east and west of the Shillong Plateau since the last earthquakes in those areas. Although the risk of a large earthquake in the near future in the segment north of the Shillong Plateau is probably less than that in the segments of the range to the east or west, the 1897 earthquake may not have relieved the strain in that segment as well. Given the evidence that the 1897 earthquake was a very large earthquake, however, it seems unlikely that there will be a repeat of such an event in the next hundred years, or more.

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Peter Molnar ¹

Affiliations
1 Department of Geological Sciences, Cooperative Institute for Research in Environmental Science (CIRES), Univerity of Colorado at Boulder, Boulder, Colorado 80309-0399, US

Abstract

Fot virtually every mountain belt and high plateau, as well as for many topographically minor features, a credible, if not outstanding, geologist has asserted that that high tenain lose abruptly in Pliocene and/or Quaternary time. Such suggestions rely on a variety of observations that include paleobotanical finds of plant organs resembling those of taxa that now live lower, recent increases in exhumation, erosion, incision, and/or sediment-accumulation rates, "juventle landscapes," and in some cases no supporting data at all (presumably because the inference has become so widely accepted that supporting evidence is no longer needed). Regions of allegedly recent "uplift" include obviously active belts like the Himalaya and seemingly tectonically dead terrain such as Transantarctic Mountains of Antarctica, the Rocky Mountains of the Western USA, of any part of Australia, as well as belts, like the western Alps, which might be called senile, it not dead yet because rigor mortis has not yet set in. The lack of a globally synchronous change in rates of plate motion in the past few million years denies any suggestion of a globally synchronous, coordinated rise of high terrain a sensible tectonic cause. Thus, although not all inferences of recent increases in mean elevations (or whatever has been meant by the word "uplift")need be false, most surely are Global climate change offers the only globally synchronous process that could mislead so many geologists to infer a recent rise of high terrain. Deciphering how climate change forged a tectonic signature on the landscape remains a challenge for geomorphologists and tectonic geologists alike.

Keywords

Cenozoic Uplift, Mountain Belts, High Terrains, Climate.

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Peter Molnar ¹

Affiliations
1 Department of Geological Sciences, University of Colorado at Boulder, Boulder, Colorado - 80309, US

Abstract

No Abstract.

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Peter Molnar ¹

Affiliations
1 Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, US

Abstract

In his report of the damage caused by the 1905 Kangra earthquake, Middlemiss (1910) reported two zones of relatively high intensity: a major one with a maximum near Kangra and Dharamsala and extending southeast to Mandi, and a minor one centered around Dehra Dun. A re-examination of the information that he gave suggests that the intervening zone of low intensity was not well-defined and that the intensity near Dehra Dun was not markedly higher than that at towns in the plains of northern India. Thus, these observations allow three different possibilities for the extent of the rupture zone. The rupture may have extended southeast 280 km, from west of Dharamsala to southeast of Dehra Dun. In this case the rupture probably occurred on segments of two thrust faults connected by a strike-slip fault in the hanging wall (or by a buried lateral ramp) north of Simla. Possibly there were two separate ruptures: one extending from near Dharamsala southeast to Mandi and the other, poorly defined, near Dehra Dun. Finally the distribution of destruction allows for the possibilities that only the area 100km in extent, from west of Dharamsala to Mandi, ruptured and that the 1905 earthquake did not relieve much strain in the region near Dehra Dun. Accordingly, it probably is safe to assume that Dharamsala will not lie in the epicentral area of the next great earthquake in the Himalaya, but it probably would be unwise to assume that that area will not include Dehra Dun.

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