Collaborative Research: Mechanisms of transient deformation following great 2006-2007 Kuril earthquakes: Frictional afterslip or viscoelastic relaxation?

合作研究：2006-2007 年千岛大地震后的瞬态变形机制：摩擦后滑还是粘弹性松弛？

• 批准号: 1014679
• 负责人: Mikhail Kogan
• 金额: $ 18.22万
• 依托单位: Columbia University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2010
• 资助国家: 美国
• 起止时间: 2010-08-01 至 2012-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1014679&HistoricalAwards=false
• 关键词: Collaborative; Research; Mechanisms; transient; deformation

The earthquake cycle in subduction zones includes strain accumulation caused by subduction, sudden strain release by the earthquake rupture, and postseismic time-dependent deformation. GPS observations of postseismic transients after large subduction earthquakes provide a natural experiment to study rheology of the megathrust and of the sublithospheric mantle. Scientists still disagree on what mechanism prevails in the postseismic transients: frictional afterslip on the coseismic rupture, viscoelastic relaxation in the asthenosphere, or poroelastic rebound. In 2006-2007, a doublet of great earthquakes (Mw 8) struck in the center of the Kuril subduction zone at the northwest Pacific Ocean: a thrust event at the subduction interface followed by an extensional event beneath the oceanward flank of the Kuril trench. It is probably the greatest doublet that has been observed in the era of satellite geodesy and broadband seismology. In 2006, the Kuril GPS Array was installed, which allowed to measure all components of the earthquake cycle. The data collected in 2006-2009 before and after the 2006-2007 earthquakes outlined a broad zone of postseismic deformation with initial horizontal velocities as fast as 100 mm/a, and a regional uplift. Most of the postseismic signal after the great Kuril doublet is caused by the viscoelastic relaxation of shear stresses in the weak asthenosphere. Viscoelastic relaxation was discriminated from other candidate mechanisms by the pattern of horizontal and vertical motions. We predict that the postseismic deformation will die out in about a decade after the earthquake doublet, so the preferred mechanism can be tested with observations continued for several years. Our initial results suggest large variations among subduction zones in the upper mantle viscosity, one of the most important parameters that governs the stress distribution.The focus of work during this 1-year proposal period will be to: (1) Guarantee continuity of the postseismic time series, without which all future work would be handicapped. (2) Analyze and develop models of postseismic transient deformation for a period 4?5 years after the great 2006?2007 Kuril earthquakes, revisiting or testing several assumptions made in the work so far. (3) Compare and assess geodetic and seismologic models for the two events, and include the effect of the outer rise event in models. (4) Map the space-time distribution of frictional afterslip, and in particular study how stress changes from the second event affected ongoing afterslip. (5) Model the deformation caused by the eruption of Sarychev volcano (Matua Island in the central Kurils).The project continues collaboration between the scientists of the US and Russia. The results of the project will have an impact on the region subject to disastrous earthquakes. This work and the methods we will develop are expected to lead to generally improved understanding of the earthquake potential of subduction zones and may thus ultimately lead to improved hazard estimation and mitigation elsewhere.

俯冲带的地震周期包括俯冲引起的应变积累、地震破裂引起的应变突然释放和震后时变形变。对大俯冲地震后震后瞬变的GPS观测为研究巨型地壳和次地球圈地幔的流变性提供了一个自然的实验。科学家们对震后瞬变的主要机制仍存在分歧：同震破裂上的摩擦性余滑、软流层中的粘弹性松弛，还是孔弹性反弹。2006-2007年，在西北太平洋千岛俯冲带中心发生了两次8级大地震：在俯冲界面上发生了一次逆冲事件，随后在千岛海沟向洋侧翼下方发生了一次伸展事件。这可能是在卫星大地测量和宽带地震学时代观察到的最大的双星。2006年，安装了千岛全球定位系统阵列，可以测量地震周期的所有组成部分。在2006-2007年地震前后收集的2006-2009年数据勾勒出一个宽广的震后形变区，初始水平速度高达100毫米/年，并有区域隆起。大千岛双线震后的大部分震后信号是由软流层中剪切应力的粘弹性松弛引起的。通过水平和垂直运动的模式将粘弹性松弛与其他候选机制区分开来。我们预测，震后形变将在双重地震后的大约10年内消失，因此首选的机制可以通过连续几年的观测来检验。我们的初步结果表明，俯冲带之间的上地幔粘度差异很大，这是控制应力分布的最重要的参数之一。在这一年的建议期内，工作的重点将是：(1)保证震后时间序列的连续性，否则未来的所有工作都将受到阻碍。(2)分析和建立2006-2007年千岛大地震后4.5年的震后瞬时形变模型，重新检验或检验目前工作中提出的几个假设。(3)对两次地震的大地测量模型和地震学模型进行了比较和评价，并在模型中考虑了外部隆起事件的影响。(4)绘制摩擦性余滑的时空分布图，重点研究第二次地震的应力变化对正在进行的余滑的影响。(5)模拟Sarychev火山(千岛群岛中部的马图亚岛)喷发造成的变形。该项目继续美国和俄罗斯科学家之间的合作。该项目的结果将对遭受灾难性地震的地区产生影响。这项工作和我们将开发的方法预计将导致对俯冲带地震潜力的普遍了解，从而最终可能导致改善其他地方的危险估计和减轻。