We imaged the mantle structure beneath northern Sumatra by inverting high‐quality seismic arrival time data and using a newly developed eikonal equation‐based teleseismic tomography method. Traveltime differences between neighboring stations were reliably extracted by cross‐correlating teleseismic waveforms, which were recorded by 26 stations from January 2009 to January 2018. Both P and S wave tomographic results show the oblique subduction of the Indo‐Australian oceanic lithosphere beneath the Sunda plate. The maximum penetration depth of the subducted slab into the mantle varies roughly from 400 km in the north to 800 km in the south. The plunging fold of the subducted slab, which mimics the shape of the trench and the volcanic arc, has less curvature than that reported in the literature; additionally, our results suggest that the gentle slab fold can be traced to a depth of about 500 km. Furthermore, a slab tear may exist beneath northern Sumatra.

An eikonal equation-based tomography method is used to invert the high-quality regional and teleseismic traveltime data recorded by 26 broadband seismic stations in northern Sumatra, following which we obtain the P and S wave velocity structures of the crust and mantle down to a depth of 800 km. The results of both P and S wave tomography clearly show that the Indo-Australian oceanic plate continuously penetrates downward beneath northern Sumatra and the maximum penetration depth varies approximately from 400 km at the northern tip of Sumatra to about 800 km around the southern boundary of our study area. Significant slab folding or bending reported in the literature as the main feature of the subducted slab beneath northern Sumatra is not found in our results. Instead, our tomographic images demonstrate only a less curved slab that mimics the shape of the Sunda Trench and volcanic arc and generally extends over depths from 120 to 450 km. P wave tomography shows broad and pronounced low-velocity anomalies beneath the island of Sumatra in the lower crust and uppermost mantle. Our model also reveals a slab tear approximately at 120-km depth, which has been documented in previous studies and considered to be related to the eruption of the Toba supervolcano.

No abstract

Sumatra is located on the western margin of Sundaland (Figure 1). According to plate reconstruction, Sumatra has been situated at its current location since the Late Jurassic (Hall, 2012). With the closure of the Neotethys Ocean, the intra-oceanic Woyla Arc accreted onto the western margin of Sundaland, forming present-day Sumatra (Advokaat et al., 2018; Hall, 2012, 2015) during the Late Cretaceous. Subduction beneath Sumatra was minimal from the Late Cretaceous to the Early Eocene, and Australia remained close to Antarctica during this period (Hall, 2012). Based on magnetic and deep-sea drilling data, the subduction of the Indo-Australian plate beneath Sumatra commenced at about 45 Ma when Australia separated from Antarctica (Hall, 2012). At that time, oblique subduction began in the Sumatra subduction zone (Beaudry & Moore, 1985; Sclater & Fisher, 1974). Studies on the deposition of sediment offshore of northern Sumatra and in the vicinity of the Sunda Strait indicate that rapid subduction may have begun in the early Miocene (∼20 Ma) (Beaudry & Moore, 1985; Malod et al., 1995). The convergence rate may have peaked in the Pliocene, as was inferred from the intense andesitic volcanism during that period; a high rate of convergence has characterized this subduction zone ever since (Hochstein & Sudarman, 1993). At present, the rate of oblique convergence in the Sumatra subduction zone is approximately 7.2 mm/yr in the south and decreases to 5.2 mm/yr in the north (Figure 1) (Sieh & Natawidjaja, 2000). Moreover, unlike the oblique subduction at the Sumatra trench, the subduction occurring in western Java is normal to the trench axis (Figure 1); consequently, there is an abrupt transition from normal subduction to oblique subduction at the Sunda Strait (Malod et al., 1995). As pointed out by Malod et al. (1995), this abrupt transition is governed by the convergence motion of the Indo-Australian and Southeast Asian plates.

Farming development have direction to improve production in order to fulfil food need and industry need in domestic, to improve export, to extend job opportunity and to push business opportunity at same time to improve farmer income so that will be expected to analyze the effect of production factors covering farm wide, fertilizer, pesticide, labour and technology, toward improvement on farm production result aand to analysis technical efficiency, price and economic, production factors have effect on paddy production at Subak Carik Tangis, Tabanan -Bali. Population in this study was the farmer in the Subak Carik Tangis as much 137 people. Sampling in this study was proportional random sampling as much 58 farmer. Data analysi method by using production faunction of Cobb-Douglas that estimated toward production factor by using multiple regression analysis with ordinary least square (OLS) regression. The results showed that simultaneously almost all rice production factors within the Cobb-Douglas production function in rice farming have a significant effect on rice production. Seed production factors, land area, urea fertilizer, and technology have significant effect on rice production. Matador pesticides and labour have no significant effect on rice production. Result of technical efficiency analysis, all production factors are technically efficient, seed production factor, land area, fertilizer, pesticide, and labour technically efficient. Viewed from the efficiency of prices, all production factors are not efficient or efficient, in which case the use of inputs is used excessively so it needs to be reduced to obtain maximum profit. Viewed from the economic efficiency all production factors are not efficient that its means the use of input is not optimal, so farmers have not gained the maximum profit. If farmers want rice yields to have a real effect, then rice farmers in Subak Carik Tangis Wongaya Gede Tabanan need to think about the production factors that will be used to obtain profits that will increase rice production maximally. In conducting rice farming, the government needs to pay attention to the factors that will affect on rice production so as to achieve efficiency in rice farming. The use of production factors needs to be done appropriately, so that farmers are able to achieve the level of efficiency. For next researchers who will conduct research in Subak Carik Tangis, it is necessary to conduct further research on "Efficiency of usage of organic rice production factor" and "marketing strategy of rice production result especially Red Rice". ABSTRAKPembangunan pertanian memiliki arah untuk meningkatkan produksi dalam rangka memenuhi kebutuhan pangan dan kebutuhan industri di dalam negeri, untuk meningkatkan ekspor, untuk memperluas kesempatan kerja dan untuk mendorong peluang bisnis pada saat yang sama untuk meningkatkan pendapatan petani sehingga diharapkan untuk menganalisa efek dari produksi faktor meliputi luas lahan, pupuk, pestisida, tenaga kerja dan teknologi, terhadap peningkatan hasil produksi...