Analysis of surface strains and velocities at the Pos Selim landslide

Abstract

The objectives of the study were 1) to carry out sensitivity analysis to determine the effects of different mesh geometries on the calculated surface strain field of the Pos Selim landslide; 2) to examine the strain field 2003-5 using the best mesh; 3) to examine the velocity profiles 2005-10 as compared to 2003-5; and 4) to draw conclusions about landslide mechanics.

The original data used by Wong 2010 was adopted for fulfilling objectives 1 and 2. The corrected vector data by Lam 2012 was adopted for fulfilling objective 3. The main analysis method was done by the calculation by the Excel and was presented in graph by either Excel or Surfer 6.0. Contours are constructed by hand rather than computer for greater reliability.

The strain fields for different meshes are broadly similar.

The velocity data 2003 – 2010 has been interpreted in relation to the suggestion of Puzrin & Schmid 2011 that any compression zone at the toe will be reflected in a bi-modal velocity profile. The velocity profiles are not bi-modal, suggesting no compression zone exists at the toe. This supports the field evidence, which suggests that failure had already occurred in 2003, in the sense that a rupture surface had fully formed from head to toe.

A Fault-Articulation Hypothesis has been tested using the rupture surface profiles suggested by Wu 2009. This hypothesis is “the landslide exploits existing faults and makes new ones where needed to assist articulation”. Evidence supporting the Fault-Articulation Hypothesis was found. It was found that Faults B and C were exploited for turning between different segments at South and Central Sections, where new faults T1, T2 and T3 were formed for turning in Head Graben. At North Section Fault B appears to have been exploited for turning between the Main Body and Head Graben but neither a geological nor a new fault appears to exist between the Main Body and the Toe Buttress.

The velocity profiles 2003 – 5 and 2005 – 10 were compared. It is evident that the landslide decelerated significantly during this period.