earth science

Sumatra Trench

Sumatra Trench is a earth science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Sumatra Trench rather than just read about it. In short: The Sumatra Trench is a part of the Sunda Trench or Java Trench. The Sunda subduction zone (called also: the Sumatra-Andaman subduction zone) is located in the east part of Indian Ocean, and is about 300 km (190 mi) from the southwest coast of Sumatra and Java islands.

Key takeaways

Sumatra Trench belongs to earth science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Sumatra Trench to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Sumatra Trench from memory before moving on to harder problems.

Reference excerpt

The Sumatra Trench is a part of the Sunda Trench or Java Trench. The Sunda subduction zone (called also: the Sumatra-Andaman subduction zone) is located in the east part of Indian Ocean, and is about 300 km (190 mi) from the southwest coast of Sumatra and Java islands. It extends over 5,000 km (3,100 mi) long, starting from Myanmar in the northwest and ending at Sumba Island in the southeast.

Geological settings

The Java trench was generated by the oblique subduction of the Indo-Australian plate into the Sunda plate at a rate of 61mm/y (in the south) and 51mm/y (in the north). The oceanic crust being subducted via this accretionary margin has variable ages (40 to 100 Ma) and structure along the trench. There is also research showing that arc parallel dextral strike-slip fault systems (i.e. the Great Sumatra fault) developed on the landward side of the Sunda forearc to absorb part of the dextral motions associated with the oblique plate convergence. After the disastrous 2004 Sumatran tsunami, more and more researchers begin to study this area. The trench slope is now being considered as a result of folds and faults in the area which were originated from the local seafloor deformation. Seismic profiles at Sumatra Trench shows that, the down-going Indo-Australian Plate has its slip vectors rotate to a NE direction. This indicates that the plate motion is dominated by the dextral shear inside the Indo-Australian plate in the order of 3.6–4.9 cm/yr. Transpressive deformation of the subducting plate edge is the primary to absorb the shear force. At the southeast section of this area, the Sumatra fault zone bends towards south and merges into the extensional south striking fault system of the Sumatra trait. The Sumatra Trench near the northwestern and western parts of Sumatra are defined as a high hazard region where 6.0 and 7.0 Mw magnitude earthquakes can generate quite often, i.e. every 6–12 and 10–30 years, respectively. The Sumatra Fault Zone (SFZ) is the most worth noting area on the Eurasian plate near the Sumatra Trench. Within the Sumatra Fault Zone lies the majority of the right-lateral stress from the relative motion between the Indo-Australian and Eurasian plates. The Sumatra Fault Zone meets the south trending extensional faulting system in Sunda Strait in Semangka. The fault zone can generate submarine pull-apart grabens.

Structure

In the convergent margins where accretion plays an important role, prism width varies from 40 km to 350 km. The width at Sumatra trench is controlled by sediment input and accretion rate and history. One distinguishing feature of the Sumatra subduction zone is that it has a relatively wide 120–140 km accretionary prism and a deep forearc basin (so does the rest of the whole Java subduction zone). However it does vary along the trench. The prism is broad and has a relatively shallow surface slope in the northern part, becomes steep and narrow at the central part, then becomes steep and narrow in the southern area.

Accretionary prism The inner part of the prism forms a NW-SE arc ridge offshore Sumatra with Enggano Islands being its highest point. This arc ridge has the widths of 30–60 km and is made up of 5 to 6 southward thrusting imbricated flakes. The flakes can be easily noticed due to their distinctive characteristics such as morphology, synclines, turn-overs and size. A distinctive strip-thrust fold locates on the western boundary of the accretionary wedge occurs on south of Enggano Island. A deformed and relatively thin (0.3–0.8 TWT) sedimentary layer covers almost all the subsurface areas. The scarce but still existing missing of part of the arc ridge offshore is result from extensional tectonic activities together with compression partitioning.

Forearc basin All the basement can be easily realized based on strong multiple reflections from the seafloor except some places in the north part because of the existing of some down faulted continental blocks. There is a main normal fault correlated along the Sumatra region. Offshore Sumatra continental basement underlies the seaward propagating wedges. The basin in southern Sumatra is greatly influenced by anticlines and fault zones.

North Sumatra region The North Sumatra region is defined here as the segment between 2.4–6°N. Accretionary wedges and forearcs here are very broad. A steep toe also presents. Average accretionary wedge has a width about 155–163 km, and the forearc basin has about 100–140 km thickness. Superficial average slope is about 1.2–1.3° while the outer part (about 50 km) becomes extremely steeper (3.3–3.9°) compare to the rest. Landward vergence of thrust folds, primarily frontal fold vergence is the most ubiquitous tectonic event happens at the prism bottom. Several landward vergences have been transformed into seaward. Seaward vergence is common further into the prism while landward vergent structures are more rare. The unusual structure here results in not only a strong wedge interior, but also tendency of a duplex deformation.

Central Sumatra region The central region is from 3°S–2°N in the area near Simeulue island (2–2.5°N). The prism narrows greatly with the increasing of average surface slope. This is an indication of the existence of a transition zone between North and Central Sumatra regions. In the Central Sumatra region, a wide basement high, which has connections with the N–S trending fracture zone, is being subducted and causing the generation of variations in sediment thickness across the oceanic plate. The transition zone in the Central Sumatra region is defined as 2–2.5°N, based on the abruptly changes of structure, morphology and sediment changes. The structure and morphology begin to change at 2.4°N but the sediment thickness remains unchanged until 2°N. Prism width decreases from 150 km to 100 km over less than 100 km strike during the surface slope increases from 1° to 3°. This region has variable oceanic plate topography, sediment component and seafloor hardness. Because as it goes further and further from the Bengal Fan source, the ridge and basement structure together with sediment thickness keep changing. Changes in prism morphology southward are gradual and an alternative boundary can be determined at 4–5°S, at this area the seafloor hardness is decreasing and deformation front heads towards sea.

… excerpt ends here. Continue reading the full article.

Illustrations

Worked examples

Example 1 — a first encounter with Sumatra Trench

Start with the simplest possible case. Write down what Sumatra Trench claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In earth science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Sumatra Trench before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Sumatra Trench ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Sumatra Trench

In research: Sumatra Trench appears in earth science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Sumatra Trench in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Sumatra Trench is common in secondary-school and first-year university syllabi. It links to neighbouring topics Oceanic trenches of the Indian Ocean, Subduction zones, so understanding it makes those chapters shorter.
In everyday life: Look for Sumatra Trench outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Sumatra Trench in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Sumatra Trench means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Sumatra Trench out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Sumatra Trench in simple terms?

Why does Sumatra Trench matter?

Because it connects several earth science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Sumatra Trench?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Sumatra Trench.