Laboratoire de Géologie, CNRS UMR 8538, École Normale Supérieure, Paris, France.
Science. 2013 Jun 7;340(6137):1208-11. doi: 10.1126/science.1235637.
Supershear earthquake ruptures propagate faster than the shear wave velocity. Although there is evidence that this occurs in nature, it has not been experimentally demonstrated with the use of crustal rocks. We performed stick-slip experiments with Westerly granite under controlled upper-crustal stress conditions. Supershear ruptures systematically occur when the normal stress exceeds 43 megapascals (MPa) with resulting stress drops on the order of 3 to 25 MPa, comparable to the stress drops inferred by seismology for crustal earthquakes. In our experiments, the sub-Rayleigh-to-supershear transition length is a few centimeters at most, suggesting that the rupture of asperities along a fault may propagate locally at supershear velocities. In turn, these sudden accelerations and decelerations could play an important role in the generation of high-frequency radiation and the overall rupture-energy budget.
超剪切地震破裂的传播速度快于剪切波速度。尽管有证据表明这种情况在自然界中发生过，但尚未在使用地壳岩石的实验中得到证实。我们在控制的上地壳应力条件下用 Westerly 花岗岩进行了粘滑实验。当法向应力超过 43 兆帕（MPa）时，超剪切破裂会系统地发生，其应力降约为 3 至 25 MPa，与地震学推断的地壳地震的应力降相当。在我们的实验中，亚瑞利至超剪切的过渡长度最多只有几厘米，这表明断层上的粗糙部分的破裂可能以超剪切速度在局部传播。反过来，这些突然的加速和减速可能在高频辐射的产生和整体破裂能量预算中发挥重要作用。
