EarthScope RAPID: Geodetic and seismological response to the Mineral, VA Earthquake, 23 August, 2011

EarthScope RAPID：对 VA 地震的大地测量和地震学响应，2011 年 8 月 23 日

• 批准号: 1202798
• 负责人: Frank Pazzaglia
• 金额: $ 2.83万
• 依托单位: Lehigh University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2012
• 资助国家: 美国
• 起止时间: 2012-01-01 至 2014-12-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1202798&HistoricalAwards=false
• 关键词: EarthScope; RAPID; Geodetic; seismological; response

The overall goal of this research is to instrument the central Virginia seismic zone (CVSZ) in the region surrounding the Mineral, VA earthquake with seismometers and global positioning system (GPS) receivers that are designed to record aftershocks and subtle ground movements respectively for a year. These measurements allow geoscientists to visualize the fault that ruptured on 23 August 2011 and better understand the state of stress in the crust that lead to the earthquake. Eastern North America has a long history of infrequent, but sometimes large and damaging earthquakes. Unlike the seismic activity that is concentrated along plate boundaries, earthquakes in the passive margin of eastern North America are not clearly identified with active faults nor are the processes that drive them well understood. Earthquakes in eastern North America are clustered into well-defined seismic zones, like the CVSZ where small to moderate-sized events including the Mineral, VA earthquake seem to occur every few decades. The seismic zones are interspersed with seismic gaps, one of which surrounds the nation's capitol, where there is little history of earthquake activity. One possible explanation of these observations is that the earthquakes cluster in areas because there is a localized, underlying geologic weakness in the crust that periodically releases accumulated stresses. Alternatively, the observed earthquakes, including the Mineral, VA event are all aftershocks of pre-historic, infrequent, but very large earthquakes and represent a crustal fracture healing over a period of several centuries. Examples of such earthquakes with estimated magnitudes of 7.0 or greater are known from the Charleston, SC (1886) and Grand Banks (1929) events and both of these locations are now recognized seismic zones characterized by frequent small to moderate-sized earthquakes. The tools that are being employed in this research are seven seismometers available from the Incorporated Research Institutions for Seismology (IRIS) instrument pool and two new GPS receivers that will be constructed following Plate Boundary Observatory (PBO) specifications. The small earthquakes that are now occurring in the Mineral, VA area are all aftershocks of the 23 August, 2011 main event that are migrating away from that rupture and traveling up along the fault plane towards the surface. As this happens, precise pinpointing of their location with a seismometer network builds a three-dimensional picture of the fault plane. At the same time, the GPS receivers are being positioned to record, with millimeter accuracy, the horizontal and vertical position of the ground surface on either side of the suspected fault plane. Together, the seismological and GPS geodesy data document how the crust and land surface deforms in the year following a moderate-sized earthquake. These data inform geological thinking on the state of stress in the crust that is used to constrain models of earthquake recurrence and hazards. Eastern North America requires more of this kind of research because many old faults inherited from the construction of the Appalachian Mountains and opening of the Atlantic Ocean are embedded in the crust and are evidently loaded and capable of generating earthquakes that cause structural damage and threaten human life. The ability of the geologic community to inform infrastructural engineers, planners, and communities as to the relative hazards associated with eastern North American faults and earthquakes will be greatly aided by a close and detailed study of the Mineral, VA event.

这项研究的总体目标是仪器的弗吉尼亚州中部地震带（CVSZ）周围的矿产，弗吉尼亚州地震与地震仪和全球定位系统（GPS）接收器，旨在记录余震和微妙的地面运动分别为一年。 这些测量使地球科学家能够可视化2011年8月23日破裂的断层，并更好地了解导致地震的地壳应力状态。 北美东部有着很长的历史，不经常发生地震，但有时会发生大的破坏性地震。 与地震活动集中在沿着板块边界不同，北美东部被动边缘的地震与活动断层没有明确的区别，也没有很好地理解驱动它们的过程。 北美东部的地震被聚集在定义明确的地震带中，如CVSZ，那里的小型到中型地震，包括弗吉尼亚州的Mineral地震，似乎每几十年发生一次。 地震带散布着地震间隙，其中一个围绕着国家的首都，那里几乎没有地震活动的历史。 对这些观测结果的一种可能解释是，地震在某些地区聚集，因为地壳中存在局部的、潜在的地质弱点，周期性地释放积累的应力。 另外，观察到的地震，包括矿物，VA事件都是史前的余震，罕见的，但非常大的地震，代表了几个世纪以来的地壳断裂愈合。 从南卡罗来纳州查尔斯顿（1886年）和大浅滩（1929年）事件中可以得知估计震级为7.0级或更大的此类地震的例子，这两个地点现在都是公认的地震带，其特征是频繁发生小到中等规模的地震。 在这项研究中使用的工具是七个地震仪，可从合并的研究机构为地震（IRIS）仪器池和两个新的全球定位系统接收器，将建造以下板块边界观测站（PBO）的规格。现在发生在弗吉尼亚州矿产地区的小地震都是2011年8月23日主要事件的余震，这些余震正从破裂处迁移，并沿着沿着断层面向上移动到地表。 当这种情况发生时，用地震仪网络精确定位它们的位置，就可以建立断层平面的三维图像。 与此同时，全球定位系统接收器正在定位，以毫米精度记录疑似断层平面两侧地面的水平和垂直位置。地震学和全球定位系统大地测量数据共同记录了中等规模地震后一年中地壳和陆地表面的变形情况。 这些数据为地质学关于地壳应力状态的思考提供了信息，地壳应力状态被用来约束地震复发和灾害的模型。 北美东部需要更多的这类研究，因为阿巴拉契亚山脉的建设和大西洋的开放继承了许多古老的断层嵌入地壳，显然是加载和能够产生地震，造成结构破坏和威胁人类生命。 地质界的能力，通知基础设施工程师，规划者和社区的相对危险与北美东部断层和地震将大大有助于密切和详细的研究，弗吉尼亚州的矿产事件。