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科学优先问题：什么是地震？
来源:河海大学海洋学院
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作者:秘书处
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发布时间: 2020-06-22
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2537 次浏览
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河海大学海洋学院闫兵老师应南京大学胡修棉老师的邀请，在“沉积之声”公众号上翻译了节选自美国国家研究理事会（NRC）发布的《时域地球——美国国家科学基金会地球科学十年愿景（2020-2030）》（A Vision for NSF Earth Sciences 2020-2030: Earth in Time）第4个科学优先问题。
河海大学海洋学院闫兵老师应南京大学胡修棉老师的邀请，在“沉积之声”公众号上翻译了节选自美国国家研究理事会（NRC）发布的《时域地球——美国国家科学基金会地球科学十年愿景（2020-2030）》（A Vision for NSF Earth Sciences 2020-2030: Earth in Time）第4个科学优先问题。
个人简介：
闫兵，男，本科和研究生就读于南京大学地球科学与工程学院，后赴日本静冈大学留学，获博士学位，长期从事断层活动性、古地震和构造地貌的研究。目前任职于河海大学海洋学院，主要研究方向包括活动构造与构造地貌、海底构造物理模拟实验等。
正文：
在教科书中和对大多数地球科学家而言，地震是断层面的快速滑动，它能够引起地面的突然震动，是地球内部的突然变形。然而，最近的观察表明，地震断层面的破裂并非如此简单，地球发生变形的时空尺度范围也要宽广得多，短到数秒至到数分钟的快速滑动，长到百万年尺度的板块构造。例如，近期一些地震的断层面破裂呈现出异常复杂的几何形态 (Hamling et al., 2017)；而地震监测技术的巨大进步带来了新发现，即地球还存在与一般地震明显不同的、缓慢但持续时间很短的变形 (Beroza and Ide, 2011) (见图2-8)。通过对断层及其周围区域的实地挖掘，我们已经积累了大量的综合性的地质数据，这些数据表明变形及其分布范围是多层次的，并且与深度密切相关 (Rowe and Griffith, 2015)。
这一认识促使地球科学家重新思考地震的本质及其驱动力，并且提出了一个看似简单的问题——“什么是地震？”。地球上任意尺度的运动和变形都是内应力作用的结果，而内应力也是驱动板块运动、形成山脉、塑造各种地形的动力。在应力作用下，材料如何发生脆性变形和弹性变形，我们已经有了很好的认识；但是，材料如何发生塑性变形，还有待进一步研究。
在接下来的10年，随着对材料性质的深入了解，以及结合高性能计算对地壳、岩石圈以及地幔的变形过程进行精确模拟，地球科学家们将会对地球内部各种形式的变形产生更加深刻的认识。基于这一认识，我们有望构建出一个关于地球变形的全新的、综合的框架。这一框架是以驱动地球系统的内应力和相关材料在各种尺度下的变形机制为基础的。
在对地球取得新认识的基础上，我们将不再简单地依据相邻板块的相对运动来描述板块边界；而是从地幔对流施加的控制板块运动力的角度出发，来描述板块边界的起源、本质、复杂性、以及作为断裂系统的演化过程。这一观点有可能形成一种全新的、综合的板块构造理论。它以关于板块运动的动力学和物理认识为基础，将会取代现有的以运动学和描述为主的板块构造理论。在新的板块构造理论下，板块构造和地幔对流将被视作同一物理过程的不同表现；在对材料性质有充分的认识之后，在这一物理过程中地球在内应力的作用下的变形方式也是可以预测的。
要完成这个统一理论，需要以下几个关键方面的进步：（1）将地震学和大地测量学观测与断裂带地质相结合，建立起地球响应构造应力发生变形的全面认识；（2）将野外调查和地质年代学研究相结合，查明已知断层的活动历史和地震复发周期；（3）通过野外考察查明已知断层和未填图断层的活动量在断裂系统（包括离散板块边界）演化中占据的比例；（4）通过岩石力学和流变学实验，测定描述变形所需的材料性质；（5）通过动力学模型的发展，再现观察到的各种尺度的构造变形，包括小尺度的地震、慢地震和稳态滑移到大尺度的板块运动。这些方面的进步，不仅具有引人注目的科学意义，而且对防震减灾具有重要的实际意义。
图2-8 断层的滑动速率和破裂传播速度的关系：地震事件（红色）、慢滑移事件（蓝色）和非地震事件（也称蠕滑）（绿色）。图表下半部分展示了实验室重现的滑动速率或破裂速度约束的变形机制及其结构特征。图片来源：Rowe and Griffith, 2015。
基础科学和社会实际相结合，是地球科学家们现今和将来研究的主题 (Williams et al., 2010; Davis et al., 2016; McGuire et al., 2017; Bebout et al., 2018; Huntington and Klepeis, 2018)。很多科研项目和申请书不仅仅是为了对地球进行测量，更是为了对地球内部基本物理过程及其结果获得前瞻性的认知，这对预防地震灾害具有显著的意义。地球科学家们认识到：从地震到板块运动的地球变形在任意时间尺度上都具有多样性，因此需要跨机构的、国家层面的、乃至国际化的协同合作。这一过程不仅促进了各式各样基础设施的发展——从测定材料性质的仪器到地震仪，从实体仪器到网络和个人基础设施；同时也促进了分析观测手段的进步，例如沿断层进行钻孔后人为注入流体诱发地震，然后进行观测和研究。
In textbooks and even for most Earth scientists, earthquakes are sudden motions of the Earth caused by rapid slip on planar faults. Recent observations, however, show that earthquake rupture is not simple and that deformation of the Earth occurs over a broad range of spatial and temporal scales, from the seconds and minutes associated with rapid slip to the million year scale of plate tectonics. For example, recent earthquake ruptures have expressed exceptional geometric complexity (Hamling et al., 2017), and dramatic improvements in monitoring have led to discoveries of a far broader spectrum of slow, transient deformation than represented by ordinary earthquakes (Beroza and Ide, 2011) (see Figure 2-8). Increasingly comprehensive geological records of exhumed faults and their surroundings demonstrate that deformation and its localization are multi-faceted and strongly depth-dependent (Rowe and Griffith, 2015).
This realization has led Earth scientists to reconsider the very nature of earthquakes and the dynamics that drive them, and to pose the deceptively simple question, “What is an earthquake?” Motions and deformation, regardless of scale, are Earth’s responses to the internal stresses that give rise to plate tectonics, mountains, and topography. We know the form of the equations governing deformation, but not the flow laws that govern the relevant material properties for deformation.
The promise of the coming decade is that advances in characterizing material properties, coupled with high-performance computing to carry out increasingly accurate simulations of crust, lithosphere, and mantle deformation processes, will lead to a more fundamental understanding of the full spectrum of observed deformation. With such an understanding it will be possible to construct a new comprehensive framework, rooted in the forces that drive the system and the material behavior that controls deformation at all relevant scales.
In this new view of the Earth, plate boundaries would not simply be described by their relative motions, but by their origin, nature, complexity, and evolution as fault systems in terms of the convective forces that control them. This view would represent a new comprehensive theory of plate tectonics that features a dynamic, physics-based understanding to supersede the current kinematic, descriptive framework. Plate tectonics and mantle convection would come to be seen as different manifestations of a single process, in which the Earth deforms in response to stress in predictable ways depending on material properties (Coltice et al., 2019).
This unified theory requires several key components: (1) seismic and geodetic observations that are integrated with fault zone geology to build a comprehensive understanding of deformational response to tectonic stress; (2) integrated field and geochronologic studies to determine slip histories and earthquake recurrence intervals on known faults; (3) field campaigns to determine how much motion is taken up by known and unmapped faults over the time-scales relevant to fault systems (and by extension plate boundary) evolution; (4) experiments in rock mechanics and rheology that measure the material properties needed to describe deformation; and (5) the development of dynamical models that can reproduce the spectrum of observed deformations from rapid, slow, and steady slip to plate motions. Such a multi-pronged approach is compelling from a scientific point of view, but also important due to the human consequences of earthquakes.
FIGURE 2-8 Slip rate and rupture propagation velocity for seismic (red), intermediate (blue), and aseismic (green) fault slip rates in active faults. The lower half of the plot shows experimentally reproduced deformation mechanisms and their textural signatures, with constraints in either slip rate or rupture velocity. SOURCE: Rowe and Griffith, 2015.
The combination of fundamental science and societal relevance has been a theme of recent and proposed geoscience community plans (Williams et al., 2010; Davis et al., 2016; McGuire et al., 2017; Bebout et al., 2018; Huntington and Klepeis, 2018). These projects and proposals aim not only at imaging and measuring the Earth, but also at a predictive understanding of the underlying physical processes and their consequences, with obvious implications for earthquakes as natural hazards. They recognize that the variety of processes over the full range of time scales relevant to understanding deformation in the Earth, from earthquakes to plate motions, require synergistic interagency, national, and international partnerships. The breadth of processes also motivates a diversity of infrastructure—ranging from material characterization to seismometers, from instrument-based facilities to cyber- and personnel infrastructure—as well as controlled fluid injection experiments in which a fault is drilled and instrumented in advance of an induced earthquake.
个人简介：
闫兵，男，本科和研究生就读于南京大学地球科学与工程学院，后赴日本静冈大学留学，获博士学位，长期从事断层活动性、古地震和构造地貌的研究。目前任职于河海大学海洋学院，主要研究方向包括活动构造与构造地貌、海底构造物理模拟实验等。
正文：
在教科书中和对大多数地球科学家而言，地震是断层面的快速滑动，它能够引起地面的突然震动，是地球内部的突然变形。然而，最近的观察表明，地震断层面的破裂并非如此简单，地球发生变形的时空尺度范围也要宽广得多，短到数秒至到数分钟的快速滑动，长到百万年尺度的板块构造。例如，近期一些地震的断层面破裂呈现出异常复杂的几何形态 (Hamling et al., 2017)；而地震监测技术的巨大进步带来了新发现，即地球还存在与一般地震明显不同的、缓慢但持续时间很短的变形 (Beroza and Ide, 2011) (见图2-8)。通过对断层及其周围区域的实地挖掘，我们已经积累了大量的综合性的地质数据，这些数据表明变形及其分布范围是多层次的，并且与深度密切相关 (Rowe and Griffith, 2015)。
这一认识促使地球科学家重新思考地震的本质及其驱动力，并且提出了一个看似简单的问题——“什么是地震？”。地球上任意尺度的运动和变形都是内应力作用的结果，而内应力也是驱动板块运动、形成山脉、塑造各种地形的动力。在应力作用下，材料如何发生脆性变形和弹性变形，我们已经有了很好的认识；但是，材料如何发生塑性变形，还有待进一步研究。
在接下来的10年，随着对材料性质的深入了解，以及结合高性能计算对地壳、岩石圈以及地幔的变形过程进行精确模拟，地球科学家们将会对地球内部各种形式的变形产生更加深刻的认识。基于这一认识，我们有望构建出一个关于地球变形的全新的、综合的框架。这一框架是以驱动地球系统的内应力和相关材料在各种尺度下的变形机制为基础的。
在对地球取得新认识的基础上，我们将不再简单地依据相邻板块的相对运动来描述板块边界；而是从地幔对流施加的控制板块运动力的角度出发，来描述板块边界的起源、本质、复杂性、以及作为断裂系统的演化过程。这一观点有可能形成一种全新的、综合的板块构造理论。它以关于板块运动的动力学和物理认识为基础，将会取代现有的以运动学和描述为主的板块构造理论。在新的板块构造理论下，板块构造和地幔对流将被视作同一物理过程的不同表现；在对材料性质有充分的认识之后，在这一物理过程中地球在内应力的作用下的变形方式也是可以预测的。
要完成这个统一理论，需要以下几个关键方面的进步：（1）将地震学和大地测量学观测与断裂带地质相结合，建立起地球响应构造应力发生变形的全面认识；（2）将野外调查和地质年代学研究相结合，查明已知断层的活动历史和地震复发周期；（3）通过野外考察查明已知断层和未填图断层的活动量在断裂系统（包括离散板块边界）演化中占据的比例；（4）通过岩石力学和流变学实验，测定描述变形所需的材料性质；（5）通过动力学模型的发展，再现观察到的各种尺度的构造变形，包括小尺度的地震、慢地震和稳态滑移到大尺度的板块运动。这些方面的进步，不仅具有引人注目的科学意义，而且对防震减灾具有重要的实际意义。
基础科学和社会实际相结合，是地球科学家们现今和将来研究的主题 (Williams et al., 2010; Davis et al., 2016; McGuire et al., 2017; Bebout et al., 2018; Huntington and Klepeis, 2018)。很多科研项目和申请书不仅仅是为了对地球进行测量，更是为了对地球内部基本物理过程及其结果获得前瞻性的认知，这对预防地震灾害具有显著的意义。地球科学家们认识到：从地震到板块运动的地球变形在任意时间尺度上都具有多样性，因此需要跨机构的、国家层面的、乃至国际化的协同合作。这一过程不仅促进了各式各样基础设施的发展——从测定材料性质的仪器到地震仪，从实体仪器到网络和个人基础设施；同时也促进了分析观测手段的进步，例如沿断层进行钻孔后人为注入流体诱发地震，然后进行观测和研究。
What is a earthquake?
In textbooks and even for most Earth scientists, earthquakes are sudden motions of the Earth caused by rapid slip on planar faults. Recent observations, however, show that earthquake rupture is not simple and that deformation of the Earth occurs over a broad range of spatial and temporal scales, from the seconds and minutes associated with rapid slip to the million year scale of plate tectonics. For example, recent earthquake ruptures have expressed exceptional geometric complexity (Hamling et al., 2017), and dramatic improvements in monitoring have led to discoveries of a far broader spectrum of slow, transient deformation than represented by ordinary earthquakes (Beroza and Ide, 2011) (see Figure 2-8). Increasingly comprehensive geological records of exhumed faults and their surroundings demonstrate that deformation and its localization are multi-faceted and strongly depth-dependent (Rowe and Griffith, 2015).
This realization has led Earth scientists to reconsider the very nature of earthquakes and the dynamics that drive them, and to pose the deceptively simple question, “What is an earthquake?” Motions and deformation, regardless of scale, are Earth’s responses to the internal stresses that give rise to plate tectonics, mountains, and topography. We know the form of the equations governing deformation, but not the flow laws that govern the relevant material properties for deformation.
The promise of the coming decade is that advances in characterizing material properties, coupled with high-performance computing to carry out increasingly accurate simulations of crust, lithosphere, and mantle deformation processes, will lead to a more fundamental understanding of the full spectrum of observed deformation. With such an understanding it will be possible to construct a new comprehensive framework, rooted in the forces that drive the system and the material behavior that controls deformation at all relevant scales.
In this new view of the Earth, plate boundaries would not simply be described by their relative motions, but by their origin, nature, complexity, and evolution as fault systems in terms of the convective forces that control them. This view would represent a new comprehensive theory of plate tectonics that features a dynamic, physics-based understanding to supersede the current kinematic, descriptive framework. Plate tectonics and mantle convection would come to be seen as different manifestations of a single process, in which the Earth deforms in response to stress in predictable ways depending on material properties (Coltice et al., 2019).
This unified theory requires several key components: (1) seismic and geodetic observations that are integrated with fault zone geology to build a comprehensive understanding of deformational response to tectonic stress; (2) integrated field and geochronologic studies to determine slip histories and earthquake recurrence intervals on known faults; (3) field campaigns to determine how much motion is taken up by known and unmapped faults over the time-scales relevant to fault systems (and by extension plate boundary) evolution; (4) experiments in rock mechanics and rheology that measure the material properties needed to describe deformation; and (5) the development of dynamical models that can reproduce the spectrum of observed deformations from rapid, slow, and steady slip to plate motions. Such a multi-pronged approach is compelling from a scientific point of view, but also important due to the human consequences of earthquakes.
FIGURE 2-8 Slip rate and rupture propagation velocity for seismic (red), intermediate (blue), and aseismic (green) fault slip rates in active faults. The lower half of the plot shows experimentally reproduced deformation mechanisms and their textural signatures, with constraints in either slip rate or rupture velocity. SOURCE: Rowe and Griffith, 2015.
The combination of fundamental science and societal relevance has been a theme of recent and proposed geoscience community plans (Williams et al., 2010; Davis et al., 2016; McGuire et al., 2017; Bebout et al., 2018; Huntington and Klepeis, 2018). These projects and proposals aim not only at imaging and measuring the Earth, but also at a predictive understanding of the underlying physical processes and their consequences, with obvious implications for earthquakes as natural hazards. They recognize that the variety of processes over the full range of time scales relevant to understanding deformation in the Earth, from earthquakes to plate motions, require synergistic interagency, national, and international partnerships. The breadth of processes also motivates a diversity of infrastructure—ranging from material characterization to seismometers, from instrument-based facilities to cyber- and personnel infrastructure—as well as controlled fluid injection experiments in which a fault is drilled and instrumented in advance of an induced earthquake.