COMET, School of Earth and Environment, University of Leeds, Leeds, LS2 9JT, UK.
COMET, Department of Earth Sciences, Durham University, Durham, DH1 3LE, UK.
Nat Commun. 2018 Apr 11;9(1):1392. doi: 10.1038/s41467-018-03739-2.
Earthquakes are caused by the release of tectonic strain accumulated between events. Recent advances in satellite geodesy mean we can now measure this interseismic strain accumulation with a high degree of accuracy. But it remains unclear how to interpret short-term geodetic observations, measured over decades, when estimating the seismic hazard of faults accumulating strain over centuries. Here, we show that strain accumulation rates calculated from geodetic measurements around a major transform fault are constant for its entire 250-year interseismic period, except in the ~10 years following an earthquake. The shear strain rate history requires a weak fault zone embedded within a strong lower crust with viscosity greater than ~10 Pa s. The results support the notion that short-term geodetic observations can directly contribute to long-term seismic hazard assessment and suggest that lower-crustal viscosities derived from postseismic studies are not representative of the lower crust at all spatial and temporal scales.
地震是由构造应变在事件之间积累释放引起的。卫星大地测量学的最新进展意味着我们现在可以高精度地测量这种震间应变积累。但是，当估计在数百年内积累应变的断层的地震危险时，如何解释短期大地测量观测值（在几十年内测量）仍然不清楚。在这里，我们表明，从主要转换断层周围的大地测量测量计算得出的应变积累率在其整个 250 年的震间期间是恒定的，除了在地震后的大约 10 年。剪切应变率历史需要一个弱的断层带嵌入在具有大于约 10 Pa s 的粘度的强下地壳中。结果支持了这样的观点，即短期大地测量观测值可以直接有助于长期地震危险评估，并表明从震后研究中得出的下地壳粘度根本不能代表所有空间和时间尺度的下地壳。
