Journal of researches into the natural history and geology of the countries visited during the voyage of H.M.S. Beagle round the world under the command of captain Fitz Roy

Seismic rupture produced spectacular tectonic deformation above a 400-kilometer strip of the Sunda megathrust, offshore northern Sumatra, in March 2005. Measurements from coral microatolls and Global Positioning System stations reveal trench-parallel belts of uplift up to 3 meters high on the outer-arc islands above the rupture and a 1-meter-deep subsidence trough farther from the trench. Surface deformation reflects more than 11 meters of fault slip under the islands and a pronounced lessening of slip trenchward. A saddle in megathrust slip separates the northwestern edge of the 2005 rupture from the great 2004 Sumatra-Andaman rupture. The southeastern edge abuts a predominantly aseismic section of the megathrust near the equator.

Supporting Online Material for Deformation and Slip Along the Sunda Megathrust in the Great 2005 Nias-Simeulue Earthquake

This paper describes geomorphologic evidence for the principal neotectonic features of Myanmar and its immediate surroundings. We combine this evidence with published structural, geodetic, and seismic data to present an overview of the active tectonic architecture of the region and its seismic potential. Three tectonic systems accommodate oblique collision of the Indian plate with Southeast Asia and extrusion of Asian territory around the eastern syntaxis of the Himalayan mountain range. Subduction and collision associated with the Sunda megathrust beneath and within the Indoburman range and Naga Hills accommodate most of the shortening across the transpressional plate boundary. The Sagaing fault system is the predominant locus of dextral motion associated with the northward translation of India. Left-lateral faults of the northern Shan Plateau, northern Laos, Thailand, and southern China facilitate extrusion of rocks around the eastern syntaxis of the Himalaya. All of these systems have produced major earthquakes within recorded history and continue to present major seismic hazards in the region.

Active tectonics and earthquake potential of the Myanmar region

The 2005 Mw 8.6 Nias-Simeulue earthquake was caused by rupture of a portion of the Sunda megathrust offshore northern Sumatra. This event occurred within an array of continuous Global Positioning System (GPS) stations and produced measurable vertical displacement of the fringing coral reefs above the fault rupture. Thus, this earthquake provides a unique opportunity to assess the source character- istics of a megathrust event from the joint analysis of seismic data and near-field static co-seismic displacements. Based on the excitation of the normal mode data and geodetic data we put relatively tight constraints on the seismic moment and the fault dip, where the dip is determined to be 8� to 10� with corresponding moments of 1.24 10 22 to 1.00 10 22 N m, respectively. The geodetic constraints on slip distribution help to eliminate the trade-off between rupture velocity and slip kine- matics. Source models obtained from the inversion of various combinations of the teleseismic body waves and geodetic data are evaluated by comparing predicted and observed long-period seismic waveforms (100-500 sec). Our results indicate a rela- tively slow average rupture velocity of 1.5 to 2.5 km/sec and long average rise time of up to 20 sec. The earthquake nucleated between two separate slip patches, one beneath Nias and the other beneath Simeulue Island. The gap between the two patches and the hypocentral location appears to be coincident with a local geological disrup- tion of the forearc. Coseismic slip clearly tapers to zero before it reaches the trench probably because the rupture propagation was inhibited when it reached the accre- tionary prism. Using the models from joint inversions, we estimate the peak ground velocity on Nias Island to be about 30 cm/sec, an order of magnitude slower than for thrust events in continental areas. This study emphasizes the importance of util- izing multiple datasets in imaging seismic ruptures.

Rupture kinematics of the 2005 M-w 8.6 Nias-Simeulue earthquake from the joint inversion of seismic and geodetic data

We used two tracks of ALOS PALSAR images to investigate the focal mechanism and slip distribution of the 2011 March 24, M W 6.8 Burma strike-slip earthquake. Three different SAR techniques, namely conventional interferometry, SAR pixel offsets (SPO) and multiple-aperture InSAR (MAI), were employed to obtain the coseismic surface deformation fields along the ∼30 km length of the fault rupture. Along-track measurements from SPO and MAI techniques show a high correlation, and were subsequently used to precisely determine the location and extent of the surface fault trace. The best-fitting fault model geometry derived from an iterative inversion technique suggests that the rupture occurred on a near-vertical sinistral strike-slip fault west of the Nam Ma fault with a strike of 70°. A maximum slip of 4.2 m occurs at a depth of 2.5 km, with significant slip constrained only to the upper 10 km of the crust.

/pdf/the-2011-mw-6-8-burma-earthquake-fault-constraints-provided-20f0ksivkm.pdf

The 2011 MW 6.8 Burma earthquake: fault constraints provided by multiple SAR techniques

The 1762 Arakan earthquake resulted from rupture of the northern Sunda megathrust and is one of those rare preinstrumental earthquakes for which early historical accounts document ground deformations. In order to obtain more comprehensive and detailed measurements of coseismic uplift, we conducted comprehensive field investigations and geochronological analyses of marine terraces on the two largest islands in western Myanmar. We confirm 3–4 m of coseismic coastal emergence along southwestern Cheduba Island, diminishing northeastward to less than 1 m. Farther northeast, uplift associated with the earthquake ranges from slightly more than 1 m to 5–6 m along the western coast of Ramree Island but is insignificant along the island's eastern coast. This double-hump pattern of uplift coincides with the long-term anticlinal growth of these two islands. Thus, we propose that the 1762 earthquake resulted from slip on splay faults under the islands, in addition to rupture of the megathrust. Elastic modeling implies that fault slip during the 1762 earthquake ranges from about 9 to 16 m beneath the islands and corresponds to a magnitude of M_w 8.5 if the rupture length of the megathrust is ~500 km. The island's uplift histories suggest recurrence intervals of such events of about 500–700 years. Additional detailed paleoseismological studies would add significant additional detail to the history of large earthquakes in this region.

Permanent upper plate deformation in western Myanmar during the great 1762 earthquake : implications for neotectonic behavior of the northern Sunda megathrust

Field investigations of an ancient fortress wall in southern Myanmar reveal an offset of ~6 m across the Sagaing fault, the major right-lateral fault between the Sunda and Burma plates. The fault slip rate implied by offset of this 16th-century fortress is between 11 and 18 cm yr^(–1). A palaeoseismological excavation within the fortress reveals at least two major fault ruptures since its construction. The slip rate we obtained is comparable to geodetic and geological estimates farther north, but is only 50 per cent of the spreading rate (38 mm yr^(–1)) at the Andaman Sea spreading centre. This disparity suggests that other structures may be accommodating deformation within the Burma Plate. We propose two fault-slip scenarios to explain the earthquake-rupture history of the southern Sagaing fault. Using both small offset features along the fault trace and historical records, we speculate that the southern Sagaing fault exhibits a uniform-fault-slip behaviour and that one section of the fault could generate a M7+ earthquake within the next few decades

Earthquakes and slip rate of the southern Sagaing fault: insights from an offset ancient fort wall, lower Burma (Myanmar)

Upper-plate splay fault earthquakes along the Arakan subduction belt recorded by uplifted coral microatolls on northern Ramree Island, western Myanmar (Burma)

https://dr.ntu.edu.sg/bitstream/10356/105369/1/A%20comprehensive%20assessment%20of%20ground%20motions%20from%20two%202016%20intra-slab%20earthquakes%20in%20Myanmar.pdf

Soe Min

Papers

Permanent upper plate deformation in western Myanmar during the great 1762 earthquake : implications for neotectonic behavior of the northern Sunda megathrust

Earthquakes and slip rate of the southern Sagaing fault: insights from an offset ancient fort wall, lower Burma (Myanmar)

Upper-plate splay fault earthquakes along the Arakan subduction belt recorded by uplifted coral microatolls on northern Ramree Island, western Myanmar (Burma)

A comprehensive assessment of ground motions from two 2016 intra-slab earthquakes in Myanmar