SRL 83:2 – Historical Seismologist

Posted: April 15, 2012 in Economy and Resources, Environment, Geography, History, Region, Tajikistan
Tags:

The Sarez-Pamir Earthquake and Landslide of 18 February 1911

doi:10.1785/gssrl.83.2.294

Nicholas Ambraseys1 and Roger Bilham2

  1. Department of Civil and Environmental Engineering, Imperial College, London, U.K.
  2. Department of Geological Sciences, University of Colorado, Boulder, Colorado, U.S.A.

INTRODUCTION

A hundred years ago 2.4 cubic km of rock fell from a Pamir mountainside >700 m to the valley floor, releasing potential energy equivalent to an Mw 7.8 ± 0.1 earthquake. Its fall created the world’s highest dam, impounding a 17-km3 lake that remains to this day. Seismograms recorded in Europe and Asia registered an earthquake at the approximate time of the fall, and soon after the details of the landslide had been evaluated a controversy arose concerning whether these seismograms had recorded an earthquake that had triggered the landslide, or whether the seismograms had merely registered waves generated by the potential energy release of the landslide’s impact. Boris Galitzin (1915) reasoned that the radiated energy almost exactly equaled the potential energy released by the fall, and hence represented the unique case of the hypocenter and the epicenter being identical. Otto Klotz (1916) translated Galitzin’s article with a preface underlining its importance, and Harold Jeffreys, in a 1923 article, despite revealing flaws in Galitzin’s calculations, confirmed both the approximate coincidence in location of the two events and the equality of energy release computed by Galitzin. However, that same year Richard Oldham dismissed the implications of Jeffreys’s calculations, noting that the maximum epicentral damage was offset from the landslide and that the area of felt shaking was typical of a deep earthquake. Though Oldham’s arguments were eventually to win, it would take another decade before it was realized that it was the long duration of energy release in the landslide that accounted for its apparent absence in distant seismograms. The details of the causal earthquake, and the curious equality in landslide and earthquake energy, have never been fully resolved. We attempt to do so in this article. We quantify what is known of the earthquake and trace the history of exploration and analysis of the landslide, whose effects remain a threat to Pamir populations to this day.

via SRL 83:2 – Historical Seismologist.

Advertisements

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s