Abstract In this study, we analyze 100 crustal Precordilleran earthquakes recorded in 2008 and 2009 by 52 broadband seismic stations from the SIEMBRA and ESP, two temporary experiments deployed in the Pampean flat slab region, between the Andean Cordillera and the Sierras Pampeanas in the Argentine Andean backarc region. In order to determine more accurate hypocenters, focal mechanisms and regional stress orientations, we relocated 100 earthquakes using the JHD technique and a local velocity model. The focal depths of our relocated events vary between 6 and 50 km. We estimated local magnitudes between 0.4 ≤ ML ≤ 5.3 and moment magnitudes between 1.3 ≤ Mw ≤ 5.3. Focal mechanisms were determined from new hypocenter relocations and first motion P-wave polarities. Our solutions exhibit a majority of the earthquakes with reverse faulting mechanism. Regional stress tensor from the inversion of P- and T-axis orientations, shows a maximum stress axis (σ1) almost horizontal with a strike of 85° and a minimum stress axis (σ3) almost vertical. We correlate this small-to-moderate magnitude seismicity with the presence of large basement structures beneath the Iglesia-Calingasta Basin in the west and the Eastern Precordillera in the east. The nucleation of deep earthquakes beneath the Iglesia Basin could be related to the presence of a major ramp accommodating the crustal shortening between the Frontal Cordillera and the Precordillera. The crustal seismicity beneath the Precordillera seems to correlate with west-dipping structures rooting deep into the Cuyania basement suggesting a thick-skinned basement deformation system beneath the Precordillera and its shallow thin-skinned fold and thrust belt.

中文翻译：

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使用地震宽带数据的阿根廷安第斯前科迪勒拉的地壳地震活动

摘要 在这项研究中，我们分析了 2008 年和 2009 年由 SIEMBRA 和 ESP 的 52 个宽带地震台记录的 100 次地壳 Precordilleran 地震，这两个临时实验部署在 Pampean 平板地区，位于阿根廷安第斯山脉的 Andean Cordillera 和 Sierras Pampeanas 之间。弧后区。为了确定更准确的震源、震源机制和区域应力方向，我们使用 JHD 技术和局部速度模型重新定位了 100 个地震。我们重新定位的事件的焦点深度在 6 到 50 公里之间。我们估计了 0.4 ≤ ML ≤ 5.3 之间的局部震级和 1.3 ≤ Mw ≤ 5.3 之间的力矩震级。焦点机制是根据新的震源重新定位和第一次运动 P 波极性确定的。我们的解决方案展示了大多数具有反向断层机制的地震。来自 P 轴和 T 轴方向反转的区域应力张量，显示最大应力轴 (σ1) 几乎水平，走向为 85°，最小应力轴 (σ3) 几乎垂直。我们将这种小到中等震级的地震活动与西部 Iglesia-Calingasta 盆地和东部 Precordillera 东部的大型基底结构的存在相关联。伊格莱西亚盆地下方深地震的成核可能与前科迪勒拉山脉和前科迪勒拉山脉之间存在容纳地壳缩短的主要斜坡有关。Precordillera 之下的地壳地震活动似乎与深深扎根于 Cuyania 基底的西倾结构相关，这表明 Precordillera 及其浅薄的薄皮褶皱和冲断带下方存在厚皮基底变形系统。