Uplift and Seismicity Driven by Magmatic Inflation at Sierra Negra Volcano, Galapagos Islands
Uplift and Seismicity Driven by Magmatic Inflation at Sierra Negra Volcano, Galapagos Islands
复制标题
DOI：
10.1029/2021jb022244
复制
发表时间：
2021-07-01
影响因子：
3.9
通讯作者：
Ruiz, Mario Calixto
中科院分区：
文献类型：
--
作者：
Bell, Andrew Forbes;Hernandez, Stephen;Ruiz, Mario Calixto
虽然地表隆起和地震活动性的增加在许多火山爆发之前发生，但它们的时间演变往往是复杂的，显然与机械变形模型预测的简单趋势相矛盾。在这里，我们使用连续的全球定位系统和记录在加拉帕戈斯群岛Sierra Negra火山的地震数据，来显示这座大厦是如何响应由岩浆聚集在一个浅层岩台所驱动的应力变化的。在2018年爆发之前的13年和6.5米的膨胀期间，隆起的速度有所变化。随着差应力的增大，单位隆升地震次数随总隆升呈指数增长。因此，时间地震活动率随时间的变化是总隆升和隆升率的函数。古腾堡-里希特b值随总隆升而减小。在火山爆发前的最后6个月，一系列大地震（M bbbb4）调节了断层的应力状态，每次地震后都有2-3天的静息期，从而延缓了地震活动性的增加。这些地震没有影响整体的隆升速率。火山喷发持续了2个月，沉降8.5米。恢复隆升时，单位隆升地震次数很低，b值较高，反映了断裂系统的松弛应力状态。这些观测结果表明，在高应力状态下，地壳变形变得越来越脆，并支持了基于弹脆力学的理论模型。他们认为，形变和地震活动的联合解释是预测类似火山环境下未来喷发的关键。
Although episodes of surface uplift and elevated seismicity precede many volcanic eruptions, their temporal evolution is often complex, and apparently in contradiction to simple trends predicted by mechanical deformation models. Here, we use continuous global positioning system and seismic data recorded at Sierra Negra volcano, Galapagos Islands, to show how the edifice responded to stress changes driven by magma accumulation in a shallow sill. The rate of uplift varied during the 13 years and 6.5 m of inflation before the 2018 eruption. The number of earthquakes per unit of uplift increased exponentially with total uplift as the differential stress increased. Accordingly, the temporal seismicity rate varied in time as a function of both the total uplift and the uplift rate. The Gutenberg-Richter b-value decreased as a function of total uplift. In the final six months before the eruption, a sequence of large (M > 4) earthquakes regulated the state of stress on the fault, each being followed by 2-3 days of postseismic quiescence, and retarding the increase in seismicity rate. These earthquakes did not affect the overall uplift rate. Subsidence of 8.5 m accompanied the 2-month eruption. On resumption of uplift, the number of earthquakes per unit of uplift was very low, and the b-value high, reflecting the relaxed stress state of the fault system. These observations show that crustal deformation becomes increasingly brittle at higher stress states, and supports theoretical models based on elastic-brittle mechanics. They suggest that joint interpretation of deformation and seismicity is key for forecasting future eruptions in similar volcanic settings.