Our detailed map of the Sumatran Fault Zone (SFZ) shows that the Sumatran Fault is highly segmented. Tony provided many useful scripts for the creation of the digital map of the Sumatran fault. 2-81 Plate 2.2 Shaded relief map of the Sumatran fault where it crosses the western flank of a.
Introduction
- Motivation: Scarcity of data for understanding the earthquake cycle
- Opportunities in the Sumatran plate boundary
- Content and organization of this thesis
- Neotectonics of the strike-slip Sumatran fault
- Paleogeodesy and paleoseismology of the Sumatran subduction zone
- References
This obstacle makes slip function repetition tests less conclusive than one would like [Sieh, 1996]. Along the Sumatran Fault, one of the largest and most active strike-slip faults in the world, we investigate the effect of fault geometry and discontinuities on earthquake faults. Our best estimates of the fracture zones of these historical events are shown as yellow ellipses in Figure 1.2.
Abercrombie [submitted 2001] found that this involved rupture of the subduction interface and a strike-slip fault in the subducting oceanic plate. I intended to include the most thorough analysis of the historical record of large earthquakes along the Sumatran faults, to test the influence of large step-overs and jogs in the fault on the locations of fault termini. Zachariasen, J., Palaeoseismology and Palaeogeodesy of the Sumatran Subduction Zone: A Study of Vertical Deformation Using Coral Microatolls, Ph.
Neotectonics of the Sumatran fault, Indonesia
Abstract
The 1900 km long trench-parallel Sumatran Fault captures a significant amount of the right-lateral component of the oblique convergence between the Eurasian and Indian/Australian plates from 10°N to 7°N. Our detailed fault map, consisting of topographic maps and aerial stereographic photographs, shows that, unlike many other large strike-slip faults, the Sumatran fault is highly segmented. If this is the case, other structures must have accommodated much of the right component of the oblique convergence over the past few million years.
The shape and location of the Sumatran fault and active volcanic arc are strongly correlated with the shape and nature of the underlying subducting oceanic lithosphere. Nevertheless, active volcanic centers in the Sumatran volcanic arc have not appreciably affected the geometry of the active Sumatran fault. We support previous suggestions that the geometry and nature of the subducting Investigator fracture zone influence the shape and evolution of the Sumatran fault system within the central domain.
Introduction
- Plate tectonic environment
- Motivation of this work
At its northwestern end, the Sumatran fault transforms into Andaman Sea spreading centers [Curray et al., 1979]. Thus, the orientation and magnitude of the relative motion vector vary significantly along the Sumatran part of the plate boundary (Fig. 2.1). The Sumatran fault is the most obvious candidate for accommodating the remaining component of dextral slip.
This large, submarine, parallel fault lies between the Sumatran fault and the trench and may have also captured a significant portion of the dextral component of plate motion. Until recently, the geometry of the fracture was only known of the first order (see, for example, the small-scale maps of Fitch [1972], Bellier et al.). Our first task in this research was thus to construct a modern map of the active components of the Sumatran fault line.
A modern map of the fault
- Resources and methods
- Geometry of the fault
- Major segments of the Sumatran fault
- Sunda segment (6.75°S to 5.9°S)
- Semangko segment (5.9°S to 5.25°S)
- Kumering segment (5.3°S to 4.35°S)
- Manna segment (4.35°S to 3.8°S)
- Musi segment (3.65°S to 3.25°S)
- Ketaun segment (3.35°S to 2.75°S)
- Dikit segment (2.75°S to 2.3°S)
- Siulak segment (2.25°S to 1.7°S)
- Suliti segment (1.75°S to 1.0°S)
- Sumani segment (1.0°S to 0.5°S)
- Sianok segment (0.7°S to about 0.1°N)
- Sumpur segment (Equator to 0.3°N)
- Barumun segment (0.3°N to 1.2°N)
- Angkola segment (0.3°N to 1.8°N)
- Toru segment (1.2°N to 2.0°N)
- Renun segment (2.0°N to 3.55°N)
- Tripa segment (3.2°N to 4.4°N)
- Aceh segment (4.4°N to 5.4°N)
- Seulimeum segment (5.0°N to 5.9°N)
- Other related structures
- Batee fault
- Toru fold and thrust belt
This would correspond to the northwestward translation of the forearc sliver plate along the Sumatran fault. Its northwestern termination is at one of the larger dilation steps along the Sumatran fault. Two large earthquakes caused severe damage along the Siulak segment of the Sumatran fault.
Major turns in the fault trace bound this segment of the Sumatran fault (Fig. 2.4 and Plate 2.1). Geomorphic expression of the fault is subtle and current anomalies appear to be absent. This segment represents the main active trace of the Sumatran fault through northern Aceh province (Fig. 2.4 and Plate 2.1).
Discussion, interpretations, and speculations
- Historical and future seismicity
- Offsets across the Sumatran fault and the evolution of dextral slip along the Sumatran margin
- Exemplary small to moderate offsets
- Largest geomorphic offsets
- Total offset
- Evidence of stretching near the Sunda Strait
- Plausible evolution of dextral slip along the Sumatran margin
- Tectonic model of the Sumatran plate margin
- Relationship of the Sumatran fault to the modern volcanic arc
- Relationship of the Sumatran fault to the subduction zone
Even these much abbreviated accounts suggest that geometric segmentation influences the seismic rupture of the Sumatran Fault. Thus, only about half of the Sumatran fault line can be expected to show shifts of more than a few kilometers. Two previous papers discuss stretching of the forearm near the southern terminus of the fracture.
They have not attempted a rigorous assessment of the implications of forearm geometry on total offset along the Sumatran fault line. We propose a simple extension measure across the Sunda segment graben, which establishes a minimal amount of dextral slip on the Sumatran fault. From simple volumetric balancing of the forearm wedge, we calculate ~100 km of forearm extension parallel to the Sumatran fault line.
A final constraint on the evolution of the Sumatran fault system is the Mio-Pliocene history of the forearc and outer arc regions. North of the Equator, 40 mm/yr of dextral slip was accommodated by the Sumatran fault (10 mm/yr) and the Aceh-Batee fault (30 mm/yr). The shapes of the subduction interface, the active volcanic arc, and the Sumatran fault also appear to be affected.
This general lack of connection suggests that the alignment of the Sumatran Volcanic Arc and the Sumatran Fault is purely coincidental. The local centerline of the volcanic arc changes along the course of the Sumatran fault. We suspect that the connection of only 9 out of 50 young volcanoes with the Sumatran fault is coincidental.
A similar coincidence exists between the shape of the Sumatran fault and the shape of the subduction interface that falls from its trace.
Summary, conclusions, and remaining questions
There the traces of the Sumatran fault and subduction isobaths are clearly discordant; the depth of the interface beneath the Sumatran fault ranges from ~100 to 175 km. Because of the polite relationship of the Sumatran fault to the isobaths in the northern and southern domains, we propose that the Sumatran fault formed first in those two domains, as two separate structures. 100 km of arc-parallel extension of the forearc strike-slip plate since the early Pliocene (Figs. 2.5 and 2.8).
The southern domain (from 7°S to 1°S) is the simplest and may have been added to the forearc rift plate only about 2 Myr ago by the creation of the Sumatran and Mentawai faults. Although the Sumatran Fault and the Sumatran Volcanic Arc share the same jungle, neither appears to have fundamentally influenced the location of the other. The average centerline of the volcanic arc is clearly northeast of, not at, the Sumatran fault.
Nevertheless, the few volcanic centers located on or near the Sumatran fault line are predominantly on major extension steps, which may have attracted a small percentage of arc volcanism. The dramatic bending in the modern volcanic arc between 0.7°N and 2.5°N is most likely the result of transtensional thinning of the forearm splinter plate over the past 4 million years. The broad similarity in shape of the Sumatran fault and subduction interface suggests a genetic relationship.
The broad, low-amplitude sinusoidal shape of the subduction interface is mimicked by the Sumatran fault, and along most of its trace the Sumatran fault lies above the 110- to 140-km isobaths of the subduction interface. These relations are especially correct north of 3.5°N and south of the equator, in the northern and southern regions. Our map of the Sumatran fault can serve as a starting point for a detailed analysis of the seismic hazard posed by this large structure.
Whether or not segmentation of the Sumatran fault markedly affected rifting, the answer to these questions could have a profound effect on our general understanding of the importance of structural geometry on the seismic processes of rifting.
Acknowledgments
Lawson, A., et al., The California Earthquake of April 18, 1906, Report of the State Earthquake Investigation Commission, 451 pp., Carnegie Ins. Elsewhere, Cenozoic deformation in Sumatra: Oblique subduction and the development of the Sumatran fault system, in Petroleum Geology of Southeast Asia, edited by A. Harbury, The Mentawai fault zone and deformation of the Sumatran forearm in the Nias area, in Tectonic Evolution of Southeast Asia, edited by R.
Westerveld, J., Eruptions of acid pumice and related phenomena along the Great Sumatran fault system, in Proceedings of the Pacific Science Congress, vol. 1000-1300 displacements of several tributaries of the Angkola River e Sianok River 700 excellent displacements of several crossings of Sianok. The Sumatran fault (SF) is a trench-parallel, right-lateral strike-slip fault that crosses the hanging wall block of the Sumatran subduction zone from the Sunda Strait to the spreading centers in the Andaman Sea.
An example of the approximately 1:100,000 scale aerial photographs that we used to construct most of our map of the Sumatran Fault. Map of 20 geometrically defined segments of the Sumatran Fault System and their spatial relationships to active volcanoes, major grabens and lakes. The Sumatran fault and related structures near the Sunda Strait and a bathymetric map of part of the Sunda Strait and the surrounding seabed.
The Sunda segment of the Sumatran fault line forms an 1800 m deep grab that widens southward towards the deformation front. The northwestern movement of the forearm strip along the Sumatran Fault appears to have thinned the area between the trench and the strait. Shaded relief map of the Sumatran fault where it intersects the western flank of a highly dissected volcano at about 4.2˚S.
Two of the most compelling large geomorphic displacements along the Sumatran fault, the 21 km dextral displacements of the Tripa and Meureubo rivers in northern Sumatra.
INDONESIAN OCEAN
Paleogeodetic records from microatolls above the central Sumatran subduction zone
- Introduction
- Motivation
- Sumatran active subduction
- Coral microatolls as paleoseismic and paleogeodetic instruments
- General
- The synthetic microatoll
- Method
- Paleogeodetic and paleoseismic sites
- Bendera site
- Badgugu site
- Barogang site
- Pono site
- Antinang site
- Memong site
- Tofa site
- Tanjung Anjing site
- Penang site
- Bai site
- Lago site
- Masin site
- Lambak site
- Sambulaling site
It appears that the head has been underwater for most of the past seven decades. Most of the heads appear to have been grown in the latter half of the 20th century. Its elevated nature suggests a significant emergence event early in the growth history of the microatoll.
Instead, the phenomenon of previous decades appears to have been reversed in the 15 years before the 1935 event.
