RAPID: Capturing the physics of mountain uplift near the South Alpine Fault New Zealand

虽然山脉通常被认为是景观中的固定物，但在地质时间尺度上，它们是短暂的现象，只存在于岩石隆起和侵蚀的竞争过程几乎完全平衡的地方。 在隆起超过侵蚀的地方，山的高度增加。 没有隆起，山脉最终会被侵蚀成平缓的丘陵，最终变成平坦的平原。 三种类型的过程可以解释山脉中岩石的上升。 第一种是通过挤压岩石引起的，类似于水平挤压橡皮擦，其表面将与水平收缩的量成比例地上升。第二种是由水平滑动向地下斜坡，逆冲断层，这类似于岩石上升的电梯由板块构造。 第三个过程导致岩石上升，以响应山谷的切割和河流的岩石移动。 这种上升（称为等熵线）类似于冰山从海上升起，因为其暴露的表面被温暖的空气融化。 这些过程中的每一个都导致岩石的上升，但在每种情况下损失的质量是不同的。 通过测量山脉中岩石的上升和相关的质量变化，人们可以区分这三种机制。 山顶的上升可以很容易地用GPS方法测量。山脉中质量的减少可以用重力计来测量。 PI于2000年1月在新西兰南部阿尔卑斯山进行了测量，但为了确定答案，需要进行第二次测量。GPS测量显示，在过去的15年里，高度增加了约80毫米。 2015年1月，PI将首次使用NSF绝对重力仪测量重力的减少。 除非发生地震，否则造成新西兰南部阿尔卑斯山高海拔的机制将被揭示。 然而，如果在测量之前发生地震，那么伴随着剧烈震动引发的山体滑坡的大规模运动可能会使答案变得模糊不清。因此，迫切需要获得NSF RAPID奖，并在新西兰南部阿尔卑斯山进行及时的测量。 2000年，国家科学基金会资助了新西兰16次重力绝对值测量，主要是在南阿尔卑斯山附近，利用重力（对当地密度变化敏感）和全球定位系统（不敏感）研究地震间山脉隆起的物理学。 FG 5重力仪是独一无二的无漂移重力仪，因为它使用原子钟和稳定激光测量真空中自由下落的镜子的加速度，精度达到10^-11。建议的造山机制（泊松比隆起，铲形断层滑动，或侵蚀引起的均衡隆起）与不同比例的隆起重力下降。现在，15年后，8厘米的隆起已经发生，PI计划采取相同的重力仪到相同的顶点，以确定相关的重力下降。重力仪的精度是1 µGal，重力的下降应该是27 µGal-一个显著的信噪比。紧急性与测量有关，因为如果发生当地地震，就像基督城附近的测量一样，山体滑坡可能会使重力信号模糊不清。事实上，阿尔卑斯山断层已经过了几十年的中位复发间隔，Mw 8级地震破裂的概率足够高，因此在未来几年内运行的捕获其滑动速度的设备有很大的机会这样做。虽然破裂的传播速度可以很容易地从地震仪（2.5-3.5公里/秒）量化，但地表断层的滑动速度（0.1- 10米/秒）迄今从未被测量过。在重力测量期间，将确定安装两个破裂仪的合适位置。每一个都由一个斜跨断层锚定的石墨棒组成，在断层滑动期间，石墨棒从旋转的鼓中拉出一根电线。其测量范围为13米，分辨率为0.1毫米，采样率为1秒，系统可以在太阳能电池板上无限期运行。

Although mountains are commonly considered fixtures in the landscape, at geological time-scales they are transient phenomena that exist only where the competing processes of rock uplift and erosion are almost exactly balanced. Where uplift exceeds erosion the height of mountains increase. Without uplift a mountain range will eventually be eroded to gentle hills, and eventually to a flat plain. Three types of processes can account for the rise of rocks within a mountain range. The first is caused by squeezing a rock, akin to squeezing a rubber eraser horizontally whose surface will rise in proportion to the amount of horizontal contraction. The second is caused by horizontal slip toward a subsurface ramp, a thrust fault, which is similar to rock rising on an elevator powered by plate tectonics. The third process causes rocks to rise in response to the incision of valleys and the removal of rock by rivers. This rise (known as isostasy) is similar to the rise of an iceberg from the sea as its exposed surface is melted by warm air. Each of these processes results in the rise of rocks, but the mass lost in each case is different. By measuring the rise of the rocks and the associated mass change in a mountain range one can distinguish between these three mechanisms. The rise of a mountain summit can easily be measured using GPS methods. The reduction of mass in a mountain range can be measured with a gravity meter. The PI measured both in the southern Alps of New Zealand in January 2000 but to determine the answer a second measurement is need. GPS measurements indicate the height has increased by about 80 mm in the past 15 years. In January 2015 the PI shall for the first time measure the reduction of gravity using the NSF absolute gravimeter. Unless an earthquake intervenes, the mechanisms that cause the high elevations of mountains in the southern Alps of New Zealand will be revealed. Should an earthquake occur before the measurements are undertaken, however, the answer may be rendered ambiguous by mass movements accompanying the landslides triggered by severe shaking. For this reason it is urgent to have this NSF RAPID award and make a timely measurement in the southern Alps of New Zealand. In 2000, NSF funded 16 measurements of absolute value of gravity in New Zealand, mostly near the Southern Alps to investigate the physics of interseismic mountain uplift using a combination of gravity (which is sensitive to local density variations) and GPS (which is not). The FG5 gravimeter is uniquely drift-free since it measures the acceleration of a freely falling mirror in a vacuum to an accuracy of 10^-11 using an atomic clock and a stabilized laser. Proposed mountain building mechanisms (Poissons-ratio uplift, listric fault slip, or erosion-induced isostatic uplift) are associated with different ratios of uplift to gravity decrease. Now, 15 years later, 8 cm of uplift has occurred and the PI plans to take the same gravimeter to the same summit points to determine the associated lowering in gravity. The accuracy of the gravimeter is 1 µGal, and the decrease in gravity should be about 27 µGal- a significant signal-to-noise ratio. Urgency is associated with the measurements in that should a local earthquake occur, as it did near the Christchurch measurements, landslides may render the gravity signal ambiguous. The Alpine fault is in fact many decades past its median recurrence interval and the probability of rupture in a Mw8 earthquake is sufficiently high that a device to capture its slip velocity operated in the next few years has a significant chance of doing so. Although the propagation velocity of a rupture can easily be quantified from seismometers (2.5-3.5 km/s) the sliding velocity of the surface fault (0.1-10m/s) has hitherto never been measured. During the gravity measurements suitable locations to install two rupture meters will be identified. Each consists of a graphite rod anchored obliquely across the fault, that pulls a wire from a rotating drum during fault slip. Its measurement range is 13 m, its resolution is 0.1 mm, its sampling rate is 1 s and the systems can run indefinitely on solar panels.