Abstract We report the first late Pleistocene left-lateral slip rate of the northern Chaman fault in Afghanistan based on 10Be dating of offset alluvial fan surfaces. Field mapping complemented with analysis of CORONA and ALOS PRISM satellite images and shaded relief and topographic data allows us to identify piercing points across the fault zone at two displaced alluvial fans (Ghat Bandakul and Azadkhail) at Wardak Province south of Kabul. We constrain the ages of offset alluvial fans based on 10Be terrestrial cosmogenic nuclides (TCN) dating of well-embedded quartzite sandstone boulders and cobbles. The Ghat Bandakul alluvial fans are offset at 165 ± 15 m and 235 ± 24 m, for which 10Be TCN model ages average 46.9 ± 3.5 kyr and 66.6 ± 4.9 kyr, respectively, yielding a slip rate of 3.5 ± 0.01 mm/yr. At the Azadkhail site, we identified two offset terraces. Based on 500 ± 50 m offset of geomorphic surface with 111.2 ± 10.5 kyr age, we obtain a slip rate of 4.5 ± 0.01 mm/yr. Combining the 800 ± 70 m left-lateral offset matching with an average age of 176.8 ± 17.1 kyr for the fan yields a geomorphic slip rate of 4.6 ± 0.1 mm/yr. These slip rates are considerably lower than geologically, geomorphologically, and geodetically defined slip rates previously obtained along the southern Chaman fault. These results show a clear trend of decreasing fault slip rate with increasing distance to the northeast. The observations suggest that the southern portion of the fault accommodates the majority of fault-parallel component of relative motion between the Indian and Eurasian plate. The lower slip rate of the Chaman fault in Afghanistan may be explained by the transfer of the left-lateral shear onto Gardez and Mokur faults that splay northward from the Chaman fault.

中文翻译：

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基于阿富汗喀布尔附近偏移地貌面 10Be 曝光测年的查曼断层晚更新世滑动速率

摘要 我们根据偏移冲积扇面的 10Be 测年报告了阿富汗北部查曼断层的第一个晚更新世左旋滑动速率。现场测绘与 CORONA 和 ALOS PRISM 卫星图像以及阴影浮雕和地形数据的分析相辅相成，使我们能够在喀布尔以南的瓦尔达克省的两个位移冲积扇（Ghat Bandakul 和 Azadkhail）的断层带上确定穿刺点。我们基于嵌入良好的石英岩砂岩巨石和鹅卵石的 10Be 陆地宇宙成因核素 (TCN) 测年来限制偏移冲积扇的年龄。Ghat Bandakul 冲积扇偏移在 165 ± 15 m 和 235 ± 24 m，其中 10Be TCN 模型的平均年龄分别为 46.9 ± 3.5 kyr 和 66.6 ± 4.9 kyr，产生的滑移率为 3.5 ± 0.01 mm/yr。在 Azadkhail 现场，我们确定了两个偏移梯田。基于 500 ± 50 m 地貌表面偏移和 111.2 ± 10.5 kyr 年龄，我们获得了 4.5 ± 0.01 mm/yr 的滑移率。将 800 ± 70 m 的左侧偏移匹配与风扇的平均年龄 176.8 ± 17.1 kyr 相结合，产生了 4.6 ± 0.1 mm/yr 的地貌滑移率。这些滑动速率远低于先前沿查曼断层南部获得的地质、地貌和大地测量定义的滑动速率。这些结果表明，随着距东北的距离增加，断层滑动率有明显降低的趋势。观察结果表明，断层的南部容纳了印度和欧亚板块之间相对运动的大部分平行断层分量。