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Since the 21st century, Lamreh, Aceh Besar Regency, Indonesia played an important role during the maritime silk route at the gate of the Malacca strait. This article investigates the subsurface structure of landslide-prone areas in cultural heritage based on 2D resistivity, chargeability and current density models of ERT, IP and VLF-EM methods, respectively. Field data measurements were carried out on 2 crossing profiles along the cliff suspected of experiencing landslides. The length of each profile is 220 with 4 m distance between stations. The 2D models reveal that the subsurface geological structure of Lamreh is composed of a mixed layer of clastic sediment and volcanic material at the top, followed by a layer of calcareous sandstone, and volcanic breccia at the bottom. The 3 layers are most easily distinguished in the resistivity model. The topmost layer is permeable but dry, i.e., characterized by a more resistive layer in the models. While the second layer is characterized by an intermediate conductivity and the bottom layer is highly conductive. The conductivity in these 2 layers is influenced by the degree of water content within the rocks. The chargeability models derived from IP data can distinguish between the dry layer on the surface and the saturated layer below. Meanwhile, the current density models obtained from VLF-EM data have proven the presence of fractures and faults along the profiles due to weathering as also seen in the resistivity models. [ABSTRACT FROM AUTHOR]

The application of magnetic and geoelectrical methods for archaeological study is presented in this paper. The study was intended to map near-surface structures around the Indrapatra Fort, the 16th-century fortification built during the Early Aceh Sultanate in the north of Sumatra. Some of the structures around the fort have been buried after the 2004 Indian Ocean Tsunami or even by previous paleotsunami deposits. The ground magnetic measurements were performed over an area of 6 750 m2 using a high-resolution Proton Precession Magnetometer G-19 Geometric. Total magnetic field data were acquired as a 3-m grid station along survey lines spaced 3-m apart. Total magnetic field anomalies were calculated by diurnal and International Geomagnetic Reference Field corrections. To clarify the position of objects causing the anomalies, analytical signals and tilt derivative filters have been applied to the total magnetic field anomalies. The method found several structures with contrasting physical properties to those of the surrounding material. Both filters were able to identify the presence of circular, elongated, and square anomalies around the Indrapatra site. The archaeological interpretation of such structures is in terms of wells, canals, and road floors. The structures are made of limestone boulders buried within the uppermost sand layer. The burning process to cement the boulders causes their magnetic properties to be different in contrast to the layer of sand that covers them. Based on magnetic interpretation, three geoelectrical profiles were measured crossing the targeted objects using Supersting R8/IP 56 Electrode Electric Resistivity. Wenner configuration with 1-meter electrodes spacing was applied for a better model resolution. The inverted models of apparent resistivity data show an agreement with magnetic interpretation at shallow depth. The models also imaged the depth and geometry of the objects based on the electrical resistivity properties of subsurface materials. It is expected that the structures preserved tsunamigenic deposits, so the discovery of the structures will be able to contribute to further research on paleotsunami in Aceh. [ABSTRACT FROM AUTHOR]

Indonesia's Aceh Province is an earthquake-prone area due to its location on the Great Sumatran Fault (GSF). Currently, earthquake mitigation by the local government constantly refers to the regional seismic hazard maps. However, some sources of an earthquake in the province which had caused damage to buildings and loss of human life were not easily traced to the fault on the surface. Currently, the mapping activities related to the Sumatra fault lines are only focused on the mainland. In contrast, the continuity of the GSF fault in the area of the sea and surrounding islands is very rarely studied. Weh Island is inhabited by many communities and has become a popular tourism area. This study aims to map the regional and local fault structure on the Weh Island using the gravity model plus (GGMPlus) data. We used the GGMPlus data with a resolution of 200 m for detailed mapping of regional and local faults. The 3D inversion of the GGMPlus data was carried out to obtain density parameters using two models, namely Singular Value Decomposition (SVD) and Occam optimization. The 3D inversion describes the presence of high-density rock blocks. A density value ranging between 2.72 - 2.96 gr/cm³ is interpreted as rocks with andesite-basaltic lava composition and lava or pyroclastic breccias resulting from local volcanic products as the rocks creating the island. Therefore, the zone interpreted as a local fault had a smaller density value (2.5 - 2.65 gr/cm³) than the surrounding. [ABSTRACT FROM AUTHOR]

In the northern part of Sumatra Island, Indonesia, the Great Sumatran Fault, which can cause an earthquake, was divided into two segments: the Aceh and Seulimeum. An effort to reduce the risk is mapping the fault area, especially in the region that does not clearly show the sign on the surface, e.g., in the Lamtamot area, Indonesia. Electrical resistivity is widely used to study shallow structures, but the method requires more time when applied in a large area. This research explores the potential of an extremely low frequency (very low frequency-electromagnetic; VLF-EM) method to investigate the shallow fault of the Seulimeum segment. Here, the VLF-EM is compared with other geophysical methods such as resistivity and magnetic methods. For comprehensive results, the geomorphic observation that was conducted covered outcrops of the fault and trenching sites in the geophysical study for validating the model. A similar pattern of the VLFEM and electrical resistivity data has been shown in a two-dimensional profile using data processing. The fault structure can be mapped at a distance of 20-24 m from the profile measurement, which is demonstrated by the low current density associated with the conductive zone from the VLF-EM, and low resistive anomaly in electrical resistivity. The fault can also be confirmed via magnetic intensity, which significantly increases at the same distance (20-25 m) of the VLF-EM and electrical resistivity. The geomorphic observation shows outcrops of fault activity, such as fault scarp, fractures, and faults, in the same direction as the Seulimeum segment, while scrap extends in the northwest direction up to ~20 m around the geophysical surveys. As revealed by the results, the VLF-EM method combined with other geophysical surveys and geomorphic observation can be used as a technique to image the fault that shows the shallow structure of the Seulimeum fault at 20-32 m along the profile. [ABSTRACT FROM AUTHOR]

River deltas are strongly affected by demographic growth and by the intensification of land use. The migration of deltaic coastlines is often rapid, threatening urban settlements, coastal farming, and coastal biotopes. Some deltas benefit from centuries of monitoring, such that the evolution of their coastline is well documented. For most deltas, however, such long records do not exist. The study of their geomorphological evolution can benefit from overlapping maps drafted over time, combined with aerial photographs and satellite images, to track the evolution of fluvial and coastal landforms. Both fluvial and coastal landforms are sensitive to variations in water and sediment supply, such that covariations in the evolution of these landforms, or the lack thereof, provide clues on the contribution of water and sediment supply to delta evolution. We document the evolution of river channels and coastlines in the delta of the Aceh River in northwest Sumatra, by overlying maps, ortho‐rectified aerial photographs, and satellite images covering the past 130 years. We assess the accuracy of the overlays, and then use multivariate statistics to analyze the co‐evolution of fluvial and coastal landforms. We propose that a progressive decrease in sediment supply spurred river channel lengthening and narrowing, landward migration of the shoreline, and narrowing of beach ridges. The 2004 Indian Ocean tsunami generated an instantaneous retreat of the coastline that amounts to ∼53% of the coastal retreat from 1884 to 2019 ce. Post‐tsunami evolution is marked by an irreversible acceleration of previous trends. Beach ridges located up‐drift of rivers and tidal channel mouths are more sensitive to long‐term landward retreat and tsunamigenic erosion. [ABSTRACT FROM AUTHOR]

This study presents a distinctive type of Muslim gravestone found on the northern coast of Sumatra, Indonesia, that dates to the 15th century. These grave markers, locally known as plang-pleng, provide evidence for the formation and disappearance of an early form of vernacular Muslim material culture in Southeast Asia. We documented over 200 of these gravestones during a large-scale archaeological landscape survey. In this article, we present a typology of these gravestones based upon shape, morphology and ornamentation. We then discuss their geographical distribution and periodisation based on examples with dated Arabic inscriptions. Our results show that these gravestones were initially a cultural product of the historic trading settlement of Lamri dating from the early 15th century. By the middle of the 15th century, variations of these stones started to appear widely near the Aceh river. The plang-pleng tradition was displaced in the early 16th century by the batu Aceh gravestones associated with the Aceh sultanate, which became a standardised part of Muslim material culture in the region for the next two centuries. [ABSTRACT FROM AUTHOR]

In order to increase the geothermal exploration, the magnetotelluric (MT) method has been used to study the subsurface of the Seulawah Agam volcano, Aceh Province, Indonesia. Similar to all resistivity methods that are based on measuring the electric field on the surface, the MT commonly contains a static shift problem, which is caused by the heterogeneities near the surface and the different topography of the volcano. The static effect can be expressed as a vertical shift from the apparent resistivity curve. In this study, the apparent resistivity data from the 1D inversion of the Transient Electromagnetic (TEM) method were used to correct the static shift problem in the MT data. Both methods were acquired in the same site at ten stations along with a 12 km distance profile that crosses the Seulawah Agam volcano. The north-south profile of the volcano area appeared to host a geothermal system. The 1D inversion in the TEM data shows a low resistivity layer that indicated a cap rock with a thickness up to 1000 m. The area below the cap rock is estimated to be a reservoir zone while the 2D inversion of MT shows that the deep conductor below 2000 m could be the heat source for the Seulawah Agam geothermal system. [ABSTRACT FROM AUTHOR]

Archaeological evidence shows that a predecessor of the 2004 Indian Ocean tsunami devastated nine distinct communities along a 40-km section of the northern coast of Sumatra in about 1394 CE. Our evidence is the spatial and temporal distribution of tens of thousands of medieval ceramic sherds and over 5,000 carved gravestones, collected and recorded during a systematic landscape archaeology survey near the modern city of Banda Aceh. Only the trading settlement of Lamri, perched on a headland above the reach of the tsunami, survived into and through the subsequent 15th century. It is of historical and political interest that by the 16th century, however, Lamri was abandoned, while low-lying coastal sites destroyed by the 1394 tsunami were resettled as the population center of the new economically and politically ascendant Aceh Sultanate. Our evidence implies that the 1394 tsunami was large enough to impact severely many of the areas inundated by the 2004 tsunami and to provoke a significant reconfiguration of the region's political and economic landscape that shaped the history of the region in subsequent centuries. [ABSTRACT FROM AUTHOR]