Spatio-temporal evolution of afterslip following the Mw 7.8 Pedernales earthquake, Ecuador

<p>We use 40 continuous GPS stations in Ecuador to quantify 3 years of the  post-seismic deformation that followed the Mw 7.8 April 16 Pedernales earthquake. We perform a kinematic inversion solving for the daily slip along the subduction to retrieve the afterslip evolution through time and space.</p><p>Rolandone et al. (2018) had found that the afterslip during the first 30 days following the earthquake was abnormally large and rapid, mainly developing at discrete patches north and south updip of the co-seismic rupture. We find that large slip and slip rate continue at both location, decreasing through time. However, models suggest that modulations of slip rate occur within those areas, with episods of slip acceleration sometimes associated with the occurrence of moderate size aftershocks.  Aside these patches, afterslip developed updip the co-seismic rupture between the patches and downdip of the coseismic rupture, with little slip occurring within the co-seismic rupture.</p><p>The overall model confirms a model of a seismic asperity encompassed in a subduction interface releasing stress through aseismic processes. However, some areas experiencing afterslip appear to be locked before the earthquake. Furthermore, those areas experienced SSE before the earthquake and during the afterslip period, raising the question of the friction parameter controlling their behavior.</p><p>In terms of moment, the amount of afterslip after 3 years is equivalent to 90% of the moment released by the Pedernales earthquake. This observation highlights that aseismic slip has an important contribution to the balance of slip during the earthquake cycle along the central Ecuador segment. This observation strengthens the proposed hypothesis of earthquake an super-cycle in central Ecuador (Nocquet et al., 2017), by confirming that the occurrence of three successive major earthquakes within 110 years exceeds the moment accumulation as derived from a decade of interseismic coupling models spanning a decade before the 2016 earthquake.</p>

Salt activity and diapirism during the Paleogene in the Baronnies Orientales (South-East basin, France) : paleogeographic and structural implications.

<p>The external Alps record a whole Wilson cycle that began at early Mesozoïc times by an extensional phase leading to the deposition of thick marine deposits upon an upper Triassic basement including a thick salt layer. Several diapiric structures (e.g. Astoin, the Barre de Chine ; Célini et al., 2020) are the witnesses of this important salt activity during deposition and the subsequent deformation through the Lower Jurassic. Otherwise, Triassic salt allowed thrusting on several decollement levels and emplacement of major thrusted units, such as the “Nappe de Digne” or the Authon thrust sheet, during the alpine phase s.s, initiated at the Oligocene-Miocene boundary. Between these two periods, the external Alps story is more uncertain and none salt activity has been clearly demonstrated except westwards in the Vocontian basin. In the whole South-East basin, only few clues, as bipyramidal quartz found in Priabonian deposits in the western Baronnies suggest a potential salt activity at surface during the Paleogene. However, in the St-Geniez areas, some Oligocene sediments, located at the vicinity of salt structures suggest a potential diapiric growth during this period. Indeed, some stratigraphic gypsum beds are found in an Oligocene lacustrine series, directly thrusted by the Authon thrust sheet.  None evaporite environments are described in the whole region at Oligocene times, which suggest a possible recycling of Triassic evaporites.</p><p>In order to determine if theses deposits are related to a Paleogene salt activity, a multi-analytical approach was used. First, a field study allowed characterizing the facies and the sedimentary filling and defining the stress regime during the deposit, by kinematic inversion on fractures which indicates a constant N-S compression during the Oligocene. The presence of halophilic fauna at the base of the lacustrine series of the St-Geniez area attests for saline influences during deposit. Moreover, 4km to the SW, a wedge in the conglomerates of the alpine continental molasse (so called red molasse) resting directly on Sorine’s Triassic diapir was put forward. Cargneules and dolomites from the Triassic constitute an important part of the reworked material. These observations indicate that the Sorine's diapir was active during the deposition of the Oligocene series. Then, a precise chemostratigraphic framework was determined by use of δ<sup>13</sup>C and δ<sup>18</sup>O isotopic data on the lacustrine limestones. <sup>87</sup>Sr/<sup>86</sup>Sr isotopic ratio on gypsum beds of the lacustrine series aimed at determining their ages and a possible Triassic evaporite sourcing. Our results gave an age ranging from 6 to 23 Ma, which does not correspond with the Oligocene age of the overlying and underlying sediments. Moreover, the large variation in isotope ratios suggests that this gypsum did not come from primary precipitation but from leaching of a pre-existing evaporite source. In conclusion, field observations, together with geochemical analyses, made it possible to highlight the relationships between tectonics, salt tectonics and sedimentation and also to reconstruct the paleogeography of the region at the end of the Paleogene.</p><p> </p><p><em>References</em></p><p><em>Célini, N., Callot, J.P., Ringenbach, J.C., Graham, R. (2020,). Jurassic salt tectonics in the SW sub-Alpine fold and thrust belt. Tectonics</em></p><p> </p>

The Mw 8.3 2015 Illapel afterslip imaged through a time-dependent inversion of continuous and survey GPS data

<div> <div> <div> <p>The Mw 8.3 2015 Illapel earthquake ruptured a 190 km long segment of the Chilean subduction zone. In the past, this area ruptured several times through large and great earthquakes, the most recent event before 2015 being a Mw 7.9 earthquake in 1943. Here, we combine continuous and survey GPS ground displacements to perform a kinematic inversion of the two-months afterslip following the mainshock. We show that the postseismic slip developed South and North of the coseismic rupture, but also overlaps the deeper part of it. We estimate that two months after the large mainshock, the postseismic moment released represents 13% of the coseismic moment (the mainshock released 3.16x10<sup>21</sup> N.m whereas the afterslip released 3.98x10<sup>20</sup> N.m). At a first order, seismicity and areas experiencing afterslip match together and are concentrated at the edges of the coseismic rupture between 25 and 45 km depth. One interesting feature is the occurrence of two moderate size aftershocks on November, 11<sup>th</sup> at shallow depth North of the rupture. We investigate the relationship between the evolution of afterslip and these aftershocks. Finally, we interpret the result in the light of past earthquakes history and calculate the moment balance through the last centuries.</p> </div> </div> </div>

2017-2019 SSE sequence and its interaction with large earthquakes in Mexico

<p><span>An intriguing sequence of a 2-stage SSE in Guerrero and a simultaneous SSE in Oaxaca took place in Mexico in 2017-2019. Three large earthquakes occur during these SSEs adding complexity to the observed surface deformations. The objective of this work is to explain the interaction between the overlapping seismic and aseismic events through the analysis of continuous GPS observations.</span></p> <p><span>We perform kinematic inversion of the GPS time series solving for the cumulative slip distribution on the subduction interface due to two SSEs, using Independent Component Analysis Inversion Method (ICAIM, Gualandi, 2015). The daily position time series for 2017-2019 are obtained by processing continuous data using GAMIT/GLOBK 10.7 (Herring et al, 2018). Strong postseismic signals generated by the following earthquakes 08/09/2017 Mw8.2 in Tehuantepec, 19/09/2017 Mw7.1 in Puebla-Morelos and 16/02/2018 Mw7.2 in Pinotepa are removed using the ICA decomposition. </span></p> <p><span>Our results show complex slip evolution on the subduction interface. We observe a clear change of cumulative seismic moment release rate after large seismic events of 2017 and after the earthquake in Pinotepa in 2018. The occurrence of Mw8.2 and Mw7.1 events notably slowed down the slip propagation of the Guerrero SSE. Continuous SSE in Oaxaca propagates from the northeast near the city of Oaxaca (-97.00°E, 16.70°N) towards the southwest approaching Pinotepa (-98.00°E, 17.00°N). Guerrero SSE migrates from the origin of its 1<sup>st</sup> phase near Tecpan (-100.50°E, 17.50°N) southeastwards to Acapulco (-99.50°E, 17.20°N) where the 2<sup>nd</sup> stage develops. Therefore the stress changes induced by the two aseismic events likely triggered the Mw7.2 Pinotepa earthquake (-98.01°E, 16.22°N). </span></p>

Geometric Method of Spatial Linkages Synthesis for Function Generation With Three Finite Positions

This paper presents a geometric method as a unified synthesis process of function generation for spatial linkages. The synthesis method utilizes the mapping relationship between spatial kinematic geometric model and two-plane projection system to transform the problem from spatial geometry to plane geometry. In this way, the synthesis process of mechanisms can be simplified through the corresponding transformation. Afterward, the line-guidance model is built up. Combining the kinematic inversion in two-plane projection system, this model can be used to realize the spatial linkages synthesis for function generation with three finite positions. Finally, revolute–sphere–sphere–revolute (RSSR) and revolute–sphere–sphere–prism (RSSP) mechanisms are offered to illustrate the application of this method.

3D numerical modelling of the Wilson cycle: structural inheritance of alternating subduction polarity

Alternating subduction polarity along suture zones has been documented in several orogenic systems. Yet the mechanisms leading to this geometric inversion and the subsequent interplay between the contra-dipping slabs have been little studied. To explore such mechanisms, 3D numerical modelling of the Wilson cycle was conducted from continental rifting, breakup and oceanic spreading to convergence and self-consistent subduction initiation. In the resulting models, near-ridge subduction initiating with the formation of contra-dipping slab segments is an intrinsically 3D process controlled by earlier convergence-induced ridge swelling. The width of the slab segments is delimited by transform faults inherited from the rifting and ocean floor spreading stages. The models show that the number of contra-dipping slab segments depends mainly on the size of the oceanic basin, the asymmetry of the ridge and variations in kinematic inversion from divergence to convergence. Convergence velocity has been identified as a second-order parameter. The geometry of the linking zone between contra-dipping slab segments varies between two end-members governed by the lateral coupling between the adjacent slab segments: (1) coupled slabs generate wide, arcuate linking zones holding two-sided subduction; and (2) decoupled slabs generate narrow transform fault zones against which one-sided, contra-dipping slabs abut.

Minimum-Jerk Trajectory Planning of a 3-DOF Translational Parallel Manipulator

Since jerk-limiting is universally recognized to possess the advantages of reducing residual vibration and improving accuracy, this paper utilizes a minimum-jerk trajectory planning algorithm in trajectory planning of a three degree-of-freedom 3-Prismatic-Universal-Universal (3PUU) translational parallel manipulator. The trajectory execution time is set to fixed time duration. The sequence of joint positions are derived by a series of predefined via-points in Cartesian space through kinematic inversion. In order to generate a trajectory featuring great continuity and fine smoothness, a piecewise fifth-order polynomial is used to interpolate the joint position series and generate a smooth trajectory characterized by continuous velocity, acceleration, and jerk. The minimum jerk trajectory planning algorithm, which minimizes the maximum of the absolute value of joints’ jerk, is actually a constrained minimax optimization problem. Subjecting to the specified limitations of kinematic constraints, this multi-variables constrained optimization problem is solved by the sequential quadratic programming (SQP) strategy. The simulated results demonstrate that this trajectory planning algorithm for the designed parallel manipulator is effective and feasible.

Synthesis of Planar Mechanisms for Pick and Place Tasks With Guiding Positions

A novel dimensional synthesis technique for solving the mixed exact and approximate motion synthesis problem for planar RR kinematic chains is presented. The methodology uses an analytic representation of the planar RR dyad's rigid body constraint equation in combination with an algebraic geometry formulation of the exact synthesis for three prescribed positions to yield designs that exactly reach the prescribed pick and place positions while approximating an arbitrary number of guiding positions. The result is a dimensional synthesis technique for mixed exact and approximate motion generation for planar RR dyads. A solution dyad may be directly implemented as a 2R open chain or two solution dyads may be combined to form a planar 4R closed chain, also known as a planar four-bar mechanism. The synthesis algorithm utilizes only algebraic geometry and does not require the use of a numerical optimization algorithm or a metric on elements of SE(2); the group of planar displacements. Two implementations of the synthesis algorithm are presented; computational and graphical construction. Moreover, the kinematic inversion of the algorithm is also included. Two examples that demonstrate the synthesis technique are included.