Extending the Spatiotemporal Scales of Physics-Based Seismic Hazard Analysis

概率地震危险性分析(PSHA)所需的时空尺度上的地震模拟是地球科学中一些最困难的计算挑战。PSHA是许多工程和社会应用的科学基础：基于性能的设计、抗震加固、恢复力工程、保险费率设定、灾害准备和预警、应急响应和公共教育。这个项目将把确定性地震模拟扩展到2赫兹和更高的地震频率，目的是减少基于物理的PSHA中的认知不确定性。这项研究将解决基本的科学问题，这些问题限制了当前源物理、滞弹性和地质非均质性表示的尺度范围。这项研究将完善地震过程的物理表示和地震模拟的确定性代码，这将有利于世界范围内的地震系统科学。在高危险级别时，平均超越概率的下降可能高达一个数量级，这将对风险降低策略的优先顺序和经济成本产生广泛影响。先前对Blue Waters的研究已经验证了模拟代码的可扩展性和计算准备情况。这些代码将用于通过数值实验和大规模模拟的协调计划推进基于物理的PSHA，该计划针对三个主要目标：(1)对照历史地震的地震记录验证高频模拟；(2)计算洛杉矶地区的高频CyberShake灾害模型，以支持美国地质调查局和南加州地震中心(SCEC)编制高分辨率城市地震危险图；以及(3)对圣安德烈亚斯断层7.8级地震的高频模拟，以修订2008年加州大地震情景，并改进为该情景详细制定的风险分析。完成这项研究的计划有五个计算里程碑：(A)包括断层粗糙度和近断层塑性的8赫兹动态破裂模拟；(B)为验证模型而对历史地震进行最高达4赫兹的模拟；(C)为验证和确认1994年北岭地震而模拟最高达8赫兹的地震；(D)将2008年ShakeOut假设扩大到4赫兹；(E)计算洛杉矶地区最高达2赫兹的完整的CyberShake灾害模型。

Earthquake simulations at the spatiotemporal scales required for probabilistic seismic hazard analysis (PSHA) present some of the toughest computational challenges in geoscience. PSHA is the scientific basis for many engineering and social applications: performance-based design, seismic retrofitting, resilience engineering, insurance-rate setting, disaster preparation and warning, emergency response, and public education. This project will extend deterministic earthquake simulations to seismic frequencies of 2 Hz and greater with the goal of reducing the epistemic uncertainties in physics-based PSHA. The research will address fundamental scientific problems that limit the scale range in current representations of source physics, anelasticity, and geologic heterogeneity. The research will improve the physical representations of earthquake processes and the deterministic codes for simulating earthquakes, which will benefit earthquake system science worldwide. The consequent decrease in mean exceedance probabilities, which could be up to an order of magnitude at high hazard levels, would have a broad impact on the prioritization and economic costs of risk-reduction strategies.Previous research on Blue Waters has verified the scalability and computational readiness of the simulation codes. These codes will be used to advance physics-based PSHA through a coordinated program of numerical experimentation and large-scale simulation targeted at three primary objectives: (1) validation of high-frequency simulations against seismic recordings of historical earthquakes; (2) computation of high-frequency CyberShake hazard models for the Los Angeles region to support the development of high-resolution urban seismic hazard maps by the U. S. Geological Survey and the Southern California Earthquake Center (SCEC), and (3) high-frequency simulation of a M7.8 earthquake on the San Andreas fault to revise the 2008 Great California ShakeOut scenario and improve the risk analysis developed in detail for that scenario. The plan to accomplish this research has five computational milestones: (a) dynamic rupture simulations up to 8 Hz that include fault roughness and near-fault plasticity; (b) simulations of historic earthquakes up to 4 Hz for model validation; (c) simulations of the 1994 Northridge Earthquake up to 8 Hz for verification and validation; (d) extension of the 2008 ShakeOut scenario to 4 Hz; and (e) calculation of a complete CyberShake hazard model for the Los Angeles region up to 2 Hz.