Abstract Book 29th Himalaya-Karakoram- Tibet Workshop Lucca, Italy 2-4 September 2014 C. Montomoli, S. Iaccarino, C. Groppo, P. Mosca, F. Rolfo, R. Carosi (editors) 29th Himalaya-Karakoram-Tibet Workshop Lucca, Italy 2-4 September 2014 Organizing committee Rodolfo Carosi, Chiara Montomoli & Salvatore Iaccarino Organized by Dipartimento di Scienze della Terra - Università degli Studi di Pisa Dipartimento di Scienze della Terra - Università degli Studi di Torino in collaboration and with the sponsorship of Società Geologica Italiana Dipartimento di Geoscienze – Università degli Studi di Padova TecTask Committe (IUGS) Fondazione Banca del Monte di Lucca Museo Regionale di Scienze Naturali – Torino Società Italiana di Mineralogia e Petrologia Provincia di Lucca Regione Piemonte Ev-K2 – CNR Focus Himalaya Travel, Milano Under the patronage of the Consiglio Nazionale delle Ricerche Gruppo Informale di Geologia Strutturale Comune di Lucca Regione Toscana Logo of the 29th HKT workshop by Margherita Campetti Abstract Book 29th Himalaya-Karakoram- Tibet Workshop Lucca, Italy C. Montomoli, S. Iaccarino, C. Groppo, P. Mosca, F. Rolfo, R. Carosi (editors) Scientific committee 29th Himalaya-Karakoram-Tibet Workshop Prof. Rodolfo Carosi, Università di Torino, Italy Dott. Isabelle Coutand, Dalhousie University, Canada Prof. Eduardo Garzanti, Univerità di Milano Bicocca, Italy Prof. Laurent Godin, Queen's University, Canada Prof. Arvind Kumar Jain, CSIR-Central Building Research Institute, Roorkee, India Prof. Asif Khan, University of Peshavar, Pakistan Prof. Rick Law Virginia Tech University, USA Dott. Chiara Montomoli, Università di Pisa Italy Dott. Yani Najman, Lancaster University, UK Prof. Santa Man Rai, Tribhuvan University, Kathmandu, Nepal Dott. Delores Robinson, University of Alabama, USA Prof. Mike Searle, University of Oxford, Great Britain Prof. Albrecht Steck, University of Lausanne, Switzerland Prof. Igor Villa, Università di Milano Bicocca, Italy and University of Bern, Switzerland Prof. Dario Visonà, Università di Padova, Italy Table of Contents Abstracts Page 3 Index of Authors Page 175 ABSTRACTS XXIX HKT Workshop – Lucca 2-4 September 2014 – Abstract Book SIKKIM EARTHQUAKE 2011: BANGLADESH EXPERIENCE A.K.M.K. Alam * Earthquake Research Cell, Geological Survey of Bangladesh, Dhaka 1000, Bangladesh * [email protected] Bangladesh is mostly floored with Holocene alluvial and deltaic unconsolidated sediments and minor Tertiary folded sedimentary rocks, and located close to the one of the active tectonic regions of the world. Whole of Bangladesh was shaken due to Sikkim earthquake of 18 September 2011, although there was no serious damage. Because the country experienced the highest shaking during last 60 years so the necessity for an assessment on the impact of this earthquake was felt. As the epicenter of the earthquake of 6.9 magnitude was near the Indian- Eurasian plate boundary and 495 km away from Dhaka, the capital city, the assessment was made mostly on the basis of the reports published in the newspapers, information collected from different parts of the country and interviews of local people. Based on these information an intensity map of the earthquake was prepared showing how the shaking affected the people, natural bodies and artificial structures. The intensity map clearly showed that response to earthquake shaking was not only related to the distance from the epicenter and magnitude but also more related to the earth material i.e. local soil condition. The maximum intensity was estimated to be IV-V which was found in areas close to the epicentral region, and in areas of clay-rich deposits and in the Old Ganges delta. Result of the study gives a clear relationship between the earthquake shaking and response of unconsolidated sediments. 3 XXIX HKT Workshop – Lucca 2-4 September 2014 – Abstract Book CHARACTERIZING THE SUB-SURFACE GEOMETRY OF THE MAIN FRONTAL THRUST IN THE DHALKEBAR AREA OF CENTRAL NEPAL R. Almeida1 *, J. Hubbard1, P. Polivka1, D. Peterson1, S. N. Sapkota2, A. Schmid1, P. Tapponnier1, and C. Timsina2 1Earth Observatory of Singapore, Nanyang Technological University, 50 Nanyang Avenue, Block N2- 01a-15, Singapore, 639798 2 National Seismological Centre, Department of Mines and Geology, Lainchaur, Kathmandu, Nepal *[email protected] The Main Frontal Thrust (MFT) represents the most frontal surface expression of the Himalayan fold and thrust belt. It is contained within the foreland deposits of this orogenic belt, the Siwalik Group. In Nepal this structure is thought to accommodate a large majority of the convergence between India and southern Tibet (~20 mm/yr; Lave and Avouac, 2000). This conclusion was based on uplift rates of river terraces in the Siwaliks. Flights os river terraces such as these are abundant in the hanging wall of the MFT, and can be dated to determine uplift rates. However, converting these uplift rates into slip rates requires knowledge about the geometry of the MFT at depth. To better constrain this geometry as well as the slip history of the MFT, we conducted seismic reflection surveys in Central Nepal around the town of Bardibas. Previous surveys in the research area have used surface data and shallow trenches to identify the surface rupture of the great 1934 earthquake (Sapkota et al., 2013). The seismic surveys are intended to (1) confirm that the rupture identified at the surface is a large through-going feature at depth; (2) image the geometry and kinematics of the fault, in order to assess both the slip in the 1934 rupture, based on surface measurements, and the behavior of the fault at longer timescales, and (3) assess how the many fault strands visible at the surface interact at depth. Ultimately, we hope to improve the assessment of seismic hazard along this fault zone, which forms one of the largest natural hazards in Nepal. The surveys were conducted during a nine-week period from January through March, 2014. Using a 6300 kg vibroseis Minibuggy, we acquired ~34 km of data in three long transects cutting across the Main Frontal Thrust, with two additional shorter transects and a small hammer survey (red lines in Figure 1). The vibroseis data were acquired with a split-spread configuration, using 264 channels with 5 m spacing. The source consisted of an 8 sec sweep, which changed linearly from 10 Hz to 120 Hz. The record lengths are 6 sec. Six to twelve sweeps, depending on ambient noise, were done at each source location to improve the signal to noise ratio of the data. The seismic lines follow several of the dry river-beds in the area and generally are orthogonal to the range front. The hammer survey was done at the northern end of the vibroseis line acquired in Sir Khola using a 7 kg sledgehammer. The line had a length of 200 m and 96 channels were used with a spacing of 2 m. We used 10 hammer swings at each source location. The hammer survey was acquired to constrain the shallow (down to ~20 m depth) location of a thrust fault in the river bed of Sir Khola (Figure 1). Preliminary processing of this data suggests that the fault is readily observable in the shallow subsurface. The Siwalik Group is strongly folded in this region. Measurements of bedding attitudes were done throughout the area to complement the seismic data (Figure 1). The bedding planes are consistently tilted with a NW-SE strike. The faults at the surface are mostly E-W. This discrepancy suggests the possibility of an oblique ramp in the thrust fault. The folding near the outcropping faults is asymmetric, typically with narrow steep fore-limbs and wide shallow back- limbs. The river terraces, however, are sub-horizontal and uplifted over large areas. This difference suggests a transition from fault-propagation folding to translation along the fault sometime before the formation of the terraces, although in a few locations the terraces are also gently folded. We expect to use the serial cross-sections obtained from the seismic data to generate a pseudo-3D view of the fault system in the area to help constrain this transition as well as any complexities in the fault-ramp structure. We plan to acquire additional seismic reflection data along other portions of the MFT in the winter of 2014-2015 to gain a better understanding of how the geometry and behavior of the fault changes along strike. 4 XXIX HKT Workshop – Lucca 2-4 September 2014 – Abstract Book Figure 1. Topographic map of the study area showing location of acquired seismic lines (red lines) and measured bedding attitudes. References Lavé J and Avouac JP, 2000. Journal of Geophysical Research 105, 5735-5770 Sapkota SN, Bollinger L, Klinger Y, Tapponnier P, Gaudemer Y and Tiwari D, 2013. Nature Geoscience 6, 71-76 5 XXIX HKT Workshop – Lucca 2-4 September 2014 – Abstract Book HYDROLOGY, HILLSLOPE PROCESSES AND SUSPENDED SEDIMENT TRANSPORT IN THE CENTRAL HIMALAYAS OF NEPAL C. Andermann1 *, M. Struck2, N. Hovius1, J. Turowski1, O. Korup3 and R. Bista4 1German Research Centre for Geosciences GFZ, Helmholtz Centre Potsdam, Germany 2 School of Earth and Environmental Sciences, University of Wollongong, Australia 3 Institute of Earth- and Environmental Sciences, University of Potsdam, Germany 4 Nepal Electricity Authority, Kathmandu, Nepal *[email protected] Suspended sediment load in rivers is a primary proxy for present-day mean catchment denudation rates (Dadson et al., 2003). In active mountain belts denudation is generally thought to be dominated by hillslope mass wasting. In the Himalayas, strong relief and intense monsoonal rainfall provide favourable conditions for mass wasting (Korup and Weidinger, 2011). On the other hand the suspended sediment fluxes in rivers, draining such large orogens, are mainly controlled by the transport capacity of these rivers and by the contribution of material from the adjacent hillslopes, for example by landsliding. In the Himalayas the spatio-temporal distribution of precipitation has numerous consequences for surface processes, water availability and transport capacities of the rivers.