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International audience; The terminal migration of Homo erectus in Southeast Asia during Early Pleistocene is cardinal to our comprehension of the evolution of the genus Homo. However, the limited consideration of the rapidly changing physical environment, together with controversial ages of hominin bearing sites, make it challenging to secure the necessary robust timeline. Here, we reappraise the first appearance datum of Javanese H. erectus by adding to a compilation of earlier estimates the most reliable age constraints based on cosmogenic nuclides 10 Be and 26 Al produced in situ. We find that H. erectus reached Java and dwelled at Sangiran, Java, at least ⇠1.4 Ma ago and more probably around 1.8 Ma. Using this age as a baseline, we develop a probabilistic approach to reconstruct their dispersal routes, coupling ecological movement simulations to landscape evolution models. We demonstrate that the hospitable terra firma conditions of Sundaland facilitated the prior dispersal of hominins to the edge of Java, where they conversely could not settle until the Javanese archipelago emerged from the sea and connected to Sundaland. We estimate a characteristic dispersal time of H. erectus across Sundaland of a few tens to hundreds kyrs, indicating that changes in their physical environment, whether climatic or physiographic, cannot be ignored. Our comprehensive reconstruction method to unravel the peopling timeline of SE Asia provides a novel framework to evaluate the evolution of early humans.

Earthquake doublets have been described in fault systems around the world but have not yet been confidently resolved in paleoseismic records. Our current knowledge is limited to historical occurrences, preventing researchers from uncovering potential patterns or recognizing common fault behavior. Identification of prehistoric doublets is thus of crucial importance for adequate seismic hazard assessment and risk mitigation. We developed a new methodology to reveal the sedimentary imprint of earthquake doublets in lacustrine paleoseismic records based on flow direction analysis in multipulsed turbidites, because the delayed arrival of turbidity currents originating from the same source location demonstrates the occurrence of individual triggering mechanisms. As grains tend to align in the presence of a flow, we analyzed flow directions by determining the dominant orientation of elongated grains using a combination of grain size, paleomagnetism, and high-resolution X-ray computed tomography. This methodology was applied to a turbidite deposited by the 2007 CE earthquakes in West Sumatra (Mw 6.4 and 6.3, 2 h apart), and it provides the first unmistakable sedimentary evidence for an earthquake doublet. We argue that this methodology has great potential to be applied to multipulsed turbidites in various subaquatic paleoseismic records and can reveal the occurrence of unknown earthquake sequences.

International audience; Natural hazards such as earthquakes, volcanic activity, and heavy rainfall causing floods and debris avalanches are common phenomena in many tropical settings, including the island of Sumatra, located in the Indonesian archipelago. To enhance our understanding of the recurrence of these often destructive events, we studied the sedimentary infill of two lakes in the Padang highlands, West Sumatra. This includes Lake Singkarak, a tectonically-formed lake located on a step-over of a major strike-slip fault system (the Sumatran Fault), and Lake Maninjau, a caldera lake. Both lakes are located -300 km from the Sunda subduction trench and surrounded by steep slopes and a chain of active volcanoes. Hence, considering their unique tectonic setting, these lakes may potentially record a wide range of natural hazards that affect the region. A combination of seismic-reflection pro¬files and short sediment cores revealed that both lakes indeed record various types of natural hazards, each with their own sedimentary response to a specific type of event. Lake Singkarak can be used to study past floods and major debris avalanches in addition to high-magnitude megathrust earthquakes, while traces of past intraplate earthquakes have been identified in both lakes. Furthermore, we argue that Lake Singkarak is an ideal recorder of volcanic activity in the region, while Lake Maninjau itself can pose a volcanic hazard toits surroundings as demonstrated by potential activity of the volcano below the lake

The Sumatran subduction zone exhibits strong seismic and tsunamogenic potential with the prominent examples of the 2004, 2005 and 2007 earthquakes. Here, we invert travel-time data of local earthquakes for vp and vp∕vs velocity models of the central Sumatran forearc. Data were acquired by an amphibious seismometer network consisting of 52 land stations and 10 ocean-bottom seismometers located on a segment of the Sumatran subduction zone that had not ruptured in a great earthquake since 1797 but witnessed recent ruptures to the north in 2005 (Nias earthquake, Mw = 8.7) and to the south in 2007 (Bengkulu earthquake, Mw = 8.5). The 2-D and 3-D vp velocity anomalies reveal the downgoing slab and the sedimentary basins. Although the seismicity pattern in the study area appears to be strongly influenced by the obliquely subducting Investigator Fracture Zone to at least 200 km depth, the 3-D velocity model shows prevailing trench-parallel structures at depths of the plate interface. The tomographic model suggests a thinned crust below the basin east of the forearc islands (Nias, Pulau Batu, Siberut) at ∼ 180 km distance to the trench. vp velocities beneath the magmatic arc and the Sumatran fault zone (SFZ) are around 5 km s−1 at 10 km depth and the vp∕vs ratios in the uppermost 10 km are low, indicating the presence of felsic lithologies typical for continental crust. We find moderately elevated vp∕vs values of 1.85 at ∼ 150 km distance to the trench in the region of the Mentawai Fault. vp∕vs ratios suggest an absence of large-scale alteration of the mantle wedge and might explain why the seismogenic plate interface (observed as a locked zone from geodetic data) extends below the continental forearc Moho in Sumatra. Reduced vp velocities beneath the forearc basin covering the region between the Mentawai Islands and the Sumatra mainland possibly reflect a reduced thickness of the overriding crust.