Use this URL to cite or link to this record in EThOS: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.792815
Title: Neotectonics and paleoseismologic observations along the Kyaukkyan Fault, Myanmar
Author: Crosetto, Silvia
Awarding Body: Royal Holloway, University of London
Current Institution: Royal Holloway, University of London
Date of Award: 2018
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Abstract:
The Kyaukkyan Fault is a dextral strike-slip fault, part of a complex zone of active dextral transpression that absorbs most of the northward motion of India relative to Sundaland. While much of the strike-slip displacement is localised in western Myanmar and along the prominent Sagaing Fault, significant dextral shear also occurs across the Kyaukkyan Fault, on the Shan Plateau in the east. The largest recorded earthquake in Myanmar occurred on the Kyaukkyan Fault in 1912, near Maymyo (Mw 7.7), but the fault has generated little significant seismicity since then. Despite its demonstrated seismic potential and remarkable topographic expression, the fault's neotectonic history remained for long time poorly known. Well-marked fault scarps and valleys locate the fault especially in its northernmost and southernmost part; geomorphic features related with Kyaukkyan Fault activity are sag ponds, shutter ridges, offset and beheaded streams, triangular facets and low-sinuosity mountain fronts. Geomorphic markers of young fault activity such as offset and deformed alluvial fans, wind-gaps were also identified during field observation. The fault's central section is characterised by a complex pull-apart system, whose normal border faults show signals of relatively slow neotectonic activity. In the central part of the basin, deformation of Quaternary sediments by a locally-buried cross-basin fault system includes dip-slip faulting, dextral strike-slip faulting and local transpression. This study coupled field investigations and satellite images interpretation that revealed deformation features developed along the Kyaukkyan Fault system, mostly indicative of Quaternary dextral strike-slip faulting. Field investigations included mapping of bedrock outcrops, which excluded the presence of metamorphic rocks exhumed along the fault in its central part; and Quaternary mapping, where stratigraphic logs of alluvial fans successions along the eastern mountain front of the Inle basin revealed a tectonically influenced sedimentary record. Satellite images were used in order to distinguish linear features and major topographic variations; Landsat imagery was then employed to discriminate the main lithologic groups, soil composition and water content, particularly in areas with reduced accessibility. Stream offset analysis included stream offset restoration, which was applied for a set of deflected streams in the northern area and allowed a quantitative evaluation of the cumulative offset along this segment of the fault. Holocene activity of the Kyaukkyan Fault is testified by paleoseismic investigations along its northern and central section. The northern trenching site is located at Kyaukkyan village, reported epicentre of the 1912 earthquake. Two earthquake ruptures have been observed in the trench: radiocarbon dating of charcoals collected along the offset horizons determined an age between 4660 ± 30 BP and 1270 ± 30 BP for the older seismic event associated with the rupture, and after 1270 ± 30 BP for the younger one. The trenching site along the central section is located far from the prominent basin-bounding fault, at the margin of a sub-basin of the main Inle Basin. Here two rupture events were observed, although the organic-rich nature of the sediments prevented the collection of uncontaminated material suitable for dating. The main conclusions of this project are (1) that the Kyaukkyan Fault has been active in Quaternary times, as confirmed by the observed deformed features along its trace; (2) activity in Inle Basin has migrated from the basin-bounding faults towards the centre of the basin, reflecting a mature stage of the evolution of the basin; (3) there is evidence of superficial ruptures related to seismic events in the northern section, at Kyaukkyan village, and north of Inle Lake; (4) the Kyaukkayn Fault may be accumulating strain due to northward motion of India and crustal flow, and hence being source of seismic hazard.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID: uk.bl.ethos.792815  DOI: Not available
Keywords: Myanmar ; strike-slip fault ; earthquake ; tectonic geomorphology ; paleoseismology
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