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Flying insects and swimming fishes have high efficiency and high maneuverability in air and water, respectively. Their wings and fins have evolved for many ages to adapt to propelling in the complex environment. In the paper, an integrative biomimetic robotic fish is proposed and developed, which combines the advantages of insect wings and fish fins to achieve a high agility underwater. In the robotic fish, two caudal fins were equipped at the tail of the robotic fish in parallel as the main propulsion mechanism, the opposite flapping of the two caudal fins generates mutually opposing lateral forces during cruising, which leads to a stable and high-performance swimming. In addition, two pectoral fins that mimic the function of insect wings were equipped at two sides of the robotic fish, which enhances the robotic fish maneuverability in vertical plane. Moreover, a central pattern generator (CPG) model was designed to achieve the versatile maneuvering motions, motion switching, and autonomous swimming with an obstacle avoiding ability. The experiments have demonstrated that the robotic fish can swim more stably and efficiently with versatile maneuver motions by taking advantage of the integrative propulsion mechanism. The developed robotic fish have many potential applications for its agility, stable swimming, and low-cost structure.

Triggered or induced earthquakes have been widely reported as resulting from various human activities, yet seismicity triggered by small-scale infrastructure construction is rare. Here, we report on an investigation of an extremely shallow M w 4.1 earthquake which occurred on 11 August 2016 in the Sichuan Basin (China), a region with historically low seismicity. Our seismic waveform analyses indicate an almost pure thrust focal mechanism at a centroid depth of~1 km. Furthermore, 18 Sentinel-1 synthetic aperture radar interferograms, stacked to obtain subcentimeter accuracy, reveal up to 3 cm line-of-sight deformation which overlaps with an automotive testing site constructed in 2014. Removal of 10 m of a surface rock layer during the construction may have produced an unloading effect and resulted in up to 0.11 MPa Coulomb stress changes on a blind fault, larger than the 0.01 MPa threshold typically invoked in studies of tectonic earthquakes. However, the delayed triggering still requires further investigation. Plain Language SummaryWhile induced earthquakes in the shallow part of the crust have been observed globally, a remaining knowledge gap is whether small-scale infrastructure construction can trigger earthquakes or not. We investigate these questions on an extremely shallow M w 4.1 earthquake in the eastern Sichuan Basin (China). To determine earthquake source parameters, we combine seismological data with satellite imaging. We find this thrust event ruptured at the depth of~1 km, located just beneath an automotive testing site constructed in 2014. Crucially, we note the testing site construction involved removal of a large volume of surface rock. We further analyze the stress changes produced by the unloading of the surface rock. We find a possible triggering relationship between the infrastructure construction and the occurrence of this shallow earthquake. Our results thus shed new light on the causes of shallow earthquakes associated with small-scale infrastructure construction.

The complex near trench velocity structures, characterized by strongly varying bathymetry along with seawater, can produce substantial waveform complexities for near trench earthquakes, which makes it difficult to study earthquake source parameters through waveform modeling/inversion. Here we explore these wavefield complexities via modeling teleseismic records of a Mw6.6 near coast event and a Mw6.8 near trench event in the 2015 Illapel earthquake sequence. For the near coast event, the waveforms of direct P waves at teleseismic/diffracted distances are simple, and we obtain consistent source parameters between 1D regional and teleseismic waveform inversions. In contrast, the near trench event produces stronger and longer P coda waves (>100 s), resulting in many dramatic discrepancies between the regional and teleseismic inversions, in particular for the centroid depth. We adopt a spectral element method-direct solution method hybrid approach to simulate synthetics with the complex source-side 3-D structures (bathymetry and water layer in this case) and investigate their roles in the genesis of strong P coda waves. Compared with the 1-and 2-D synthetics, the 3-D synthetics significantly improve the waveform fits up to 0.1 Hz when the source is placed at the preferred horizontal (~30 km from the trench axis) and vertical (~5 km beneath the ocean bottom) location. The refined location of the earthquake indicates that the plate interface is probably locked at very shallow depths and capable of nucleating strong earthquakes. We highlight the need for considering near trench 3-D structures in seismic waveform analysis of near trench earthquakes, many of which are tsunamigenic.Key Points:• The persisting (>100 s) and strong P coda waves of a Mw6.8 near trench event are well reproduced by the 3D modelling that incorporates bathymetry and water layer • 3D waveform modelling is used to relocate the centroid of the near trench earthquake to be 30 km away from the trench and 5 km beneath the ocean floor • Strong and long lasted coda waves of the 2015 Mw8.3 Illapel mainshock could be largely explained by the near trench structure effectsSupporting Information:• Supporting Information S1