Direct measurements of frictional heating by earthquake faulting

一组精密温度计已经部署在非常靠近即将发生地震的断层的地方。该地点位于南非一个深金矿的3公里深处，采矿正在一个主要地质断层附近进行。我们钻了许多约30米长的孔，以查明20米厚的复杂断裂带的三维结构。对岩心和钻孔视频图像进行了广泛的分析。结果表明，该断裂带存在明显的软弱面，仅在围岩与断裂带交界处约10 cm厚的部位受到严重破坏。在交叉钻孔测量的整个区域（10 x 10 m），该特征是连续的，非常平坦。我们可以在离这架飞机1米远的地方安装许多温度计。断裂带是由寄主岩石中的岩化磨蚀物组成的。然而，类平面结构非常有限。除上述边界弱面外， ...更多信息 只有少数平面显示出局部剪切的片理化构造。然而，只有上面提到的边界部分是如此脆弱，以至于该平面上的所有钻孔交叉点都有一圈来自钻孔壁的损失材料。在每个钻孔中，仅在与该边界的相交处观察到这种损坏。温度数据连续记录，表明地温具有良好的稳定性。数据的质量足够好，以解决摩擦加热的滑动低至十分之一的摩擦阻力在实验室实验中测量，如果M2-3地震，这是预期在这个矿井，发生在我们上面确定的薄弱面。这意味着我们测量的分辨率涵盖了所谓的地壳应力悖论中争论的可能强度范围。目前的观测观察到断层周围岩石温度的时间变化，这是由断层面的摩擦加热引起的。这需要地震后大约一个月的数据。观测必须非常靠近断层，这可能会受到目标地震的破坏。很可能由于地震破坏而无法使用观测仪器。因此，采取了一些措施，包括使用无线数据传输，以确保观测系统在数据记录、遥测和供电方面的故障安全。少

An array of precision thermometers has been deployed very close to the fault of impending earthquakes. The site was at a 3 km depth in a deep gold mine in South Africa, where mining is taking place near a major geologic fault. We drilled many holes of about a 30 m length to find out a three dimensional structure of complex fault zone of over a 20 m thickness. Extensive analysis of core and borehole video images was carried out. The reuslt has shown that there is a distinct plane of weakness ; only of an about 10 cm thickness part at one on the boundary between the host rock and fault zone is severely damaged. This feature was continuous and quite planar over the whole area (10 x 10 m) surveyed with the intersecting boreholes. We could install many thermometers in a 1 m distance from this plane. The fault zone consisted of the lithified attrition material deriving from the host rocks. However, the plane-like structures were very limited. Besides the boundary weak plane mentioned above, … More there were only a few planes showing a foliated structures indicateve of localized shear. However, it was only the boundary part mentioend above that was so friable that all the boreholes intersections on this plane has a ring of lost material from the borehole wall. Such a damage was observed only at the intersection with this boundary in each borehole. The temperature data were continuously recorded, which showed a good stability of the ground temperature. The quality of data was good enough to resolve the frictional heating by a sliding at as low as one tenth of the frictional resistance measured in laboratory experiments, if an earthquake of M2-3, which is expected in this mine, occurred on the plane of weakness we identified above. This means that the resolution of our measurements covers the possible range of strength argued in the so-called crustal stress paradox. The present observation watches the temporal changes of rock temperature around the fault, which is caused by the frictional heating of the fault plane. This requires data for about a month following the eartquake. The observation has to be done very close to the fault, which is likely to suffer the damage from the targeted earthquake. It is quite possible that access to the observational instruments is lost by the earthquake damage. Therefore, number of measures, including the use of wireless data transfer, were taken to fail-safe the observational system, in terms of data recording, telemetry, and power supply. Less