Time-Dependent Earthquake Forecasts with a Tectonic Basis

研究人员正在准备、发布和测试地震预报，以解决有关浅层地震活动的一些基本问题，并提高对全球地震危害的认识。每一次预报都描述了一个大区域（全球范围），甚至整个地球，并由一个（或一组）特定最小/阈值震级和特定时间段的地震概率的数字地图组成。强调大面积和中等阈值震级意味着可以将大量实际地震与每次预报进行比较，并且可以定量评估相对成功（与零假设或更简单的模型相比）。这项工作建立在两种不同的预测方法上，每一种方法都基于对地震活动的基本认识：地震在空间和时间上聚集（ETES模型）；地震发生在断层滑动和其他非弹性应变的位置（SHIFT模型）。在这个项目中，每个模型首先根据另一个模型的指导进行细化。基于详细的运动学模型，对五个构造带的短期地震聚集和触发进行了研究。此外，假定的长期地震活动性与构造速率的比例（除了在海洋中部扩张上升的情况下）正在使用考虑聚类的统计数据进行检验。下一步是合并两种预测模型，测试几种不同的可能组合，以构造为基础创建随时间变化的地震预测。最后，研究人员将确定预测方法应该从主要基于聚类转向主要基于构造的时间尺度。（这个时间可能是由当地的构造应力积累速率控制的。）每个关于地震活动性一般控制（和/或特定参数值）的假设都是通过对现有目录的回顾性测试来初步评估的。通过这些测试的假设将在地震可预测性研究合作实验室进行的正式前瞻性测试中进一步研究。该项目正在创建一种新的组合预测算法，供加州地震概率工作组和其他类似组织考虑，该算法提供了从1年和5年预测到50年和500年预测的“无缝”过渡，满足各种社会需求。如果更准确的地震预报能够在全球范围内迅速实施，潜在的下游社会效益可能是巨大的。该项目还试图解决有关地震活动性的一个最基本的问题：低地震活动性板块边界是永久的，还是暂时的？这将指导下一代关于在冷的摩擦断层上是什么控制地震和地震滑动的假设。

The investigators are preparing, publishing, and testing earthquake forecasts in order to resolve some basic questions about shallow seismicity, and improve knowledge of global seismic hazard. Each forecast describes a large region (of global scale), or even the entire Earth, and consists of a digital map (or set of maps) of earthquake probabilities for particular minimum/threshold magnitude(s) and for particular period(s) of time. The emphasis on large areas and moderate threshold magnitudes means that large numbers of actual earthquakes can be compared with each forecast, and relative success (compared to a null hypothesis or simpler model) can be evaluated quantitatively. This work builds on two different forecasting methods, each based on an elementary insight about seismicity: Earthquakes cluster in space and time (ETES model); and earthquakes occur at locations of fault slip and other anelastic strain (SHIFT model). In this project, each model is first undergoing refinement based on guidance from the other. Short-term earthquake clustering and triggering are being studied in five tectonic zones based on a detailed kinematic model. Also, the assumed proportionality of long-term seismicity to tectonic rate (except on mid-ocean spreading rises) is being tested using statistics that take account of clustering. The next step is to merge the two forecast models, testing several different kinds of possible combination, to create time-dependent earthquake forecasts with a tectonic basis. Finally, the investigators will determine the time-scales over which the forecast method should shift from primarily clustering-based to primarily tectonics-based. (This time is likely to be controlled by the local rate of tectonic stress accumulation.) Each hypothesis about general controls on seismicity (and/or specific parameter values) is initially evaluated by retrospective testing against existing catalogs. Hypotheses which pass these tests are further investigated in formal prospective tests administered by the Collaboratory for the Study of Earthquake Predictability. This project is creating a new combined forecasting algorithm for consideration by the Working Group on California Earthquake Probabilities and other similar groups, which provides a "seamless" transition from 1-year and 5-year forecasts to 50-year and 500-year forecasts, meeting a variety of social needs. The potential downstream social benefits may be large if more accurate earthquake forecasts can be quickly implemented on a global basis. The project is also attempting to resolve one of the most fundamental questions about seismicity: Whether low-seismicity plate boundaries are permanent, or temporary? This will guide the next generation of hypotheses about what controls seismic versus aseismic slip on cool, frictional faults.