Extending the Spatiotemporal Scales of Physics-Based Seismic Hazard Analysis

概率地震灾害分析（PSHA）所需的时空尺度地震模拟提出了地球科学中一些最棘手的计算挑战。PSHA是许多工程和社会应用的科学基础：基于性能的设计、抗震改造、弹性工程、保险费率设定、灾害准备和预警、应急响应和公共教育。该项目将把确定性地震模拟扩展到2 Hz及以上的地震频率，目的是减少基于物理的PSHA的认知不确定性。这项研究将解决一些基本的科学问题，这些问题限制了目前震源物理、非弹性和地质非均质性表征的尺度范围。该研究将改进地震过程的物理表征和模拟地震的确定性代码，有利于世界范围内的地震系统科学。由此造成的平均超出概率的降低，在高危险水平上可能达到一个数量级，将对减少风险战略的优先次序和经济成本产生广泛影响。先前对Blue Waters的研究已经验证了仿真代码的可扩展性和计算就绪性。这些代码将通过一个协调的数值实验和大规模模拟计划来推进基于物理的PSHA，目标有三个主要目标：(1)根据历史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）开发高分辨率城市地震灾害地图；(3)对圣安地列斯断层进行7.8级地震的高频模拟，以修订2008年加州大震荡情景，并改进该情景的详细风险分析。完成这项研究的计划有五个计算里程碑：(a)高达8 Hz的动态破裂模拟，包括断层粗糙度和近断层塑性；(b)为验证模式而进行的最高达4hz的历史地震模拟；(c) 1994年北岭地震8赫兹的模拟，以供核实和确认；(d)将2008年的“震动淘汰”方案延长至4赫兹；(e)计算洛杉矶地区高达2hz的完整的CyberShake危害模型。

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.