An earthquake sequence occurred in the Atacama region of Chile throughout September 2020. The sequence initiated by a mainshock of magnitude $M_w$= 6.9, followed 17 hours later by a $M_w$= 6.4 aftershock. The sequence lasted several weeks, during which more than a thousand events larger than $M_l$= 1 occurred, including several larger earthquakes of magnitudes between 5.5 and 6.4. Using a dense network that includes broad-band, strong motion and GPS sites, we study in details the seismic sources of the mainshock and its largest aftershock, the afterslip they generate and their aftershock, shedding light of the spatial temporal evolution of seismic and aseismic slip during the sequence. Dynamic inversions show that the two largest earthquakes are located on the subduction interface and have a stress drop and rupture times which are characteristics of subduction earthquakes. The mainshock and the aftershocks, localized in a 3D velocity model, occur in a narrow region of interseismic coupling (ranging 40%-80%), i.e. between two large highly coupled areas, North and South of the sequence, both ruptured by the great $M_w\sim$8.5 1922 megathrust earthquake. High rate GPS data (1 Hz) allow to determine instantaneous coseismic displacements and to infer coseismic slip models, not contaminated by early afterslip. We find that the total slip over 24 hours inferred from precise daily solutions is larger than the sum of the two instantaneous coseismic slip models. Differencing the two models indicates that rapid aseismic slip developed up-dip the mainshock rupture area and down-dip of the largest aftershock. During the 17 hours separating the two earthquakes, micro-seismicity migrated from the mainshock rupture area up-dip towards the epicenter of the $M_w$ 6.4 aftershocks and continued to propagate upwards at ∼ 0.7 km/day. The bulk of the afterslip is located up-dip the mainshock and down-dip the largest aftershock, and is accompanied with the migration of seismicity, from the mainshock rupture to the aftershock area, suggesting that this aseismic slip triggered the $M_w$= 6.4 aftershock. Unusually large post-seismic slip, equivalent to $M_w$= 6.8 developed during three weeks to the North, in low coupling areas located both up-dip and downdip the narrow strip of higher coupling, and possibly connecting to the area of the deep Slow Sleep Event detected in the Copiapo area in 2014. The sequence highlights how seismic and aseismic slip interacted and witness short scale lateral variations of friction properties at the megathrust.

整个 2020 年 9 月智利阿塔卡马地区发生地震序列。 ${米}_{瓦}$= 6.9，17 小时后 ${米}_{瓦}$= 6.4 余震。这个序列持续了几个星期，在此期间，超过一千个事件大于${米}_{升}$= 1 次发生，包括几次 5.5 至 6.4 级的较大地震。利用包括宽带、强震和 GPS 站点的密集网络，我们详细研究了主震的震源及其最大余震、它们产生的余震及其余震，揭示了地震和地震的时空演化在序列中滑动。动力反演表明，两次最大的地震都位于俯冲界面，具有俯冲地震特征的应力降和破裂次数。位于 3D 速度模型中的主震和余震发生在地震间耦合的狭窄区域（范围为 40%-80%），即 在序列的北部和南部的两个大的高度耦合区域之间，两者都被巨大的 ${米}_{瓦}～$8.5 1922 年特大地震。高速率 GPS 数据 (1 Hz) 允许确定瞬时同震位移并推断同震滑动模型，不受早期后滑动的影响。我们发现从精确的每日解推断出的 24 小时内的总滑移大于两个瞬时同震滑移模型的总和。区分这两个模型表明，快速地震滑动在主震破裂区上倾，最大余震下倾。在两次地震相隔的 17 小时内，微地震活动从主震破裂区向上倾斜向震中迁移。${米}_{瓦}$6.4 次余震并继续以 0.7 公里/天的速度向上传播。大部分余震位于主震上倾和最大余震下倾，并伴随着地震活动从主震破裂到余震区的迁移，表明这次抗震滑动触发了${米}_{瓦}$= 6.4 余震。异常大的震后滑动，相当于${米}_{瓦}$= 6.8 在向北的三周内形成，位于上倾和下倾的高耦合窄带的低耦合区域，并可能与 2014 年在科皮亚波地区检测到的深度慢睡眠事件区域相连。突出了地震和抗震滑动如何相互作用，并见证了巨型推力上摩擦特性的短尺度横向变化。