美国地质调查局Adrian M. Bender及其小组在研究北阿拉斯加山脉前缘的快速活动的逆冲断层上取得新进展。相关论文发表在2023年3月29日出版的《地质学》杂志上。
研究表明，阿拉斯加北部山脉下面的山麓冲断滑动，沿Denali断层的中部，吸收了现代4.4 mm/yr的大地速度梯度，相当于约百分之78的5.6 mm/yr的Yakutat会聚区的残余。地层阶地沉积物的红外激发发光年龄(674 ka; 6个点)，量化了横跨1947Mw河基岩切口在1947 Mw 7.1 逆冲地震震中区的Totatlanika河的基岩的切割。切口率在靠近盲推力段的范围前部上方，从小于1 mm/yr突然增加到4.8-5.6 mm/yr。
北阿拉斯加山脉前缘下方陡峭的逆冲斜坡上6.7 mm/yr的快速滑动适应了大地测量梯度，以与测量的切割速率相匹配的速率驱动岩石隆起，这意味着类似1947年的事件的大地震可能以500-1400年的频率重复发生。结果阐明了复杂汇聚边缘内侧的集中震应变，并提示了对阿拉斯加新构造格架的重新评价。
据介绍，板收汇聚速率强烈影响汇聚板块边缘内的地震活动和造山运动，但是适应远场汇聚的结构分布和结构运动学可能令人难以捉摸。在阿拉斯加内陆，Yakutat微板块汇聚驱动晚更新世到全新世Denali断层的右翼的滑动，但是向西递减的滑动速率使得大量残余的Yakutat运动无法解释。
附：英文原文
Title: Rapid active thrust faulting at the northern Alaska Range front
Author: Adrian M. Bender, Richard O. Lease, Tammy Rittenour, James V. Jones
Issue&Volume: 2023-03-29
Abstract: Plate convergence rates strongly influence seismicity and mountain building inboard of convergent margins, but the distribution and kinematics of structures accommodating far-field convergence can be elusive. In interior Alaska, Yakutat microplate convergence drives late Pleistocenerecent right slip on the Denali fault, but westward-decreasing slip rates leave substantial residual Yakutat motion unaccounted for. Here, we show that Northern Foothills thrust slip beneath the northern Alaska Range absorbs a modern 4.4 mm/yr geodetic velocity gradient equivalent to ～78% of the 5.6 mm/yr residual Yakutat convergence along the central Denali fault. Infrared-stimulated luminescence ages of strath terrace deposits (674 ka; six sites) quantify Totatlanika River bedrock incision across the 1947 Mw 7.1 thrust earthquake epicentral region. Incision rates increase abruptly from <1 mm/yr to 4.85.6 mm/yr above the blind thrust tip near the range front. Rapid slip at 6.7 mm/yr on a steep thrust ramp beneath the northern Alaska Range front accommodates the geodetic gradient, drives rock uplift at rates matching measured incision rates, and implies that large earthquakes like the 1947 event may recur with 5001400 yr frequency. Results illuminate focused seismogenic strain inboard of a complex convergent margin and prompt reevaluation of Alaska’s neotectonic framework.
DOI: 10.1130/G51049.1
