Rafael Almeida

Understanding the cause and location of the end‐points of thrust earthquake ruptures is critical yet unresolved question in seismic hazard assessment for convergent margins, where numerous destructive earthquakes have occurred. Here, we offer a novel perspective on rupture termination by examining the arrest of the 1906 M 8.0 Manas earthquake in northwestern China. Integrated field surveys, seismic profiles, and microseismicity data reveal that rupture terminated at the actively growing Xiaodushan anticline. This anticline lies parallel to and in the hanging wall of the seismogenic fault. We propose active folding acts as an efficient rupture‐arrest barrier, partitioning seismic energy into strata uplift and microseismicity. Furthermore, comparative analysis of global thrust earthquakes identifies two termination mechanisms: fault geometric complexities and external structural barriers. These findings contribute to deeper understanding of rupture lengths and earthquake magnitudes for seismic hazard assessment in convergent margins globally.

The Tokai area in the eastern Nankai Trough is characterized by the subduction of a rough plate interface caused by bathymetric highs related to the adjacent Izu‐Bonin arc and fault fabrics in the oceanic crust. However, the effect of this process on the structural development of its accretionary wedge and megathrust seismicity is still poorly understood. To get better insight into Tokai area we apply full‐waveform inversion to legacy wide‐angle seismic data exploiting available signal frequency up to 15 Hz. From this model we extract pseudo‐reflectivity attributes, which are complementary to the section obtained with Kirchoff pre‐stack depth migration of streamer data. The high‐resolution images reveal detailed geological characterization of the subducting oceanic crust, the geometry of the megathrust and splay faults, and the structure of the wedge. The latter is characterized by imbricate fans, out‐of‐sequence thrusts, and duplexes that significantly contribute to its thickening. We compare these features to published structural models and propose that the increased structural complexity in the Tokai segment is due to fault reactivation triggered by the subduction of the bathymetric highs. We suggest that this fault reactivation also controls the shallow seismogenic behavior of this region. We show that the evolution of the forearc basin is related to the ongoing underplating process and out‐of‐sequence thrusting within the wedge. We compare our seismic imaging results with bathymetric, magnetic, and gravity data, revealing no evidence of large ridges beneath our profile, which previous studies have proposed as a cause of the persistent Tokai seismic gap.

Over the past 424 years, the Littoral Fault Zone (LFZ), located offshore of the South China coast, has experienced four destructive earthquakes (M ≥ 7). These events have resulted in an approximately 700 km seismic gap centered on the Greater Bay Area of China, home to over 70 million people. Despite previous studies on deeper crustal structures and geodynamic processes, the shallow structural architecture and recent tectonic activity of the LFZ within the seismic gap remain poorly understood due to limited offshore geophysical investigations. Here, we present new offshore geophysical data to explore the shallow crustal architecture and Holocene activity of the LFZ within this seismic gap. Multichannel seismic data reveal that the LFZ comprises a high-angle listric main normal fault along with several secondary normal faults. The main fault trends northeast and dips southeast in the shallow crustal architecture, serving as the basin-controlling fault in the north of the Pearl River Mouth Basin, with accumulated displacements ranging from 1.5 to 1.8 km. Furthermore, analysis of single-channel seismic data, and ¹⁴C dating results from the borehole, indicate that the most recent movement of the main fault occurred within the last ~10,000 years, with minimum vertical offsets of 1.2 m. Based on these findings, we emphasize the LFZ’s potential to generate a significant earthquake, estimated at M_w 7.0–7.5, within the inferred seismic gap. Our study highlights the potential earthquake hazard posed by the LFZ to the Greater Bay Area of China, while also providing valuable insights for the assessment of active submarine faults worldwide.

The Xiongpo fault-fold belt shows prominent NE, ENE- and ~N–S-trending relief, which resulted from multi-stage upper crustal shortening in the Longmen Shan piedmont during the eastward growth of the eastern Tibetan Plateau. Previous studies have determined its 2D structural configurations from seismic profiles and field-based geological cross-sections. Here, we extend this analysis into the entire belt to explore the 3D structural evolution of this complex fault-fold belt and have built a 3D regional fault model. The results reveal along-strike variation of subsurface structural architecture of the Xiongpo fault-fold belt, which is characterized by transformation from a complex superimposition of a deep fault-bend fold beneath a shallow structural wedge in the center segment to a simple shallow fault-bend fold on both ends of the structure, and then to a trishear fault propagation fold on the plunging edges. This structural transformation determines the contrast between the NE-striking relief of the central segment, and the ENE- and ~N-S-striking relief in the two plunging zones. We combine our results with published low-temperature thermochronology and growth strata results to propose a three-stage evolution for the Xiongpo fault-fold belt that closely relates with regional stress field changes, including a NE-striking fault under the NW–SE compression between 40–25 Ma and 15–10 Ma, lateral propagation of the NE-striking fault and initiation of ENE-striking fault by WNW–ESE compression from ~5–2 Ma, ~N–S fault under ~E–W compression until the present. This work enhances our understanding of the stress field changes of eastern Tibet since the Late Eocene. It also can serve as a typical case study deciphering 3D fault-fold growth using seismic and geological imaging, which is helpful to understand 3D structural and landscape evolutions of other complex fault-fold belts worldwide.

To investigate the subsurface structure surrounding the Main Frontal Thrust (MFT) in central Nepal, we drilled and cored sediments to depths of 45-100 m at ten sites. Our boreholes were located along previously acquired high-resolution seismic profiles across the MFT imaging the upper 1-2 km of the subsurface, which revealed a beveled erosional surface in the hanging wall above a broad, gentle anticline, as well as growth strata in the footwall. The boreholes exhibit interlayered clays, silts, sands, and gravels, dated with optically stimulated luminescence and radiocarbon to <72.5±4.3 ka, with a transition from finer to coarser sediments at ~13.5±0.1 ka. Near the fault tip, the sediments exhibit steeper dips and deformation bands. A 25-m-thick section of silt and clay above the south end of the buried anticline is interpreted as a temporary lacustrine depocenter formed due to uplift near the fault tip. Based on the distribution of marker beds and sediment ages, we interpret a shortening rate of 3.1-12.1 mm/a on the MFT. Three major transitions between fluvio-lacustrine and coarse fluvial channel facies are inferred from the boreholes, and the timings of these transitions correlate with Indian monsoonal intensity variations linked to Earth’s precession. We infer that strengthened monsoon led to increased river discharge and advance of coarse bedload-dominant braided channels, whereas weak monsoon formed a finer-grained channel environment. These monsoonal climate variations have affected the depositional environment and river base levels in this region, influencing the formation and apparent relative uplift of nearby river terraces.

In this work, we present a description of the sedimentary fill of a well-exposed lacustrine succession in the Ecuadorian Andes. The Guayllabamba basin is an intermontane basin located in the Andean range of Ecuador, and part of its sedimentary history is represented by a volcanically influenced c. 100 m-thick lacustrine unit of Pleistocene age. We create a stratigraphic cross-section from the eastern to western lake margins and identify 19 facies that were used to carry out a palaeoenvironmental reconstruction. The Guayllabamba palaeolake was developed in a tectonic depression surrounded by volcanoes and it was filled with sediments derived from the erosion of the volcanic edifices, the reworking of unconsolidated pyroclastic deposits and deposition of pyroclastic currents into the lake. The lake shows a deepening trend, passing from shallow deltaic sedimentation to varved diatomites with turbidites. Abundant ash-fall beds, monolithological pumiceous deltaic sequences and pumice-dominated thick ignimbrites show the impacts of volcanism on lacustrine sedimentation within this basin. Soft-sediment deformation and gravity flow deposits are common owing to the intrabasinal tectonic activity and to the intrusion of a lava body. Aulacoseira -rich diatomites dominate the background lake sedimentation. The outcrops of the Guayllabamba basin are outstanding examples of the interaction between volcaniclastic and lacustrine sedimentation.