中国海陆水平地震背景噪音的观测和机理研究

除天然地震外的自然事件和人类活动形成了地震记录上的背景噪音，可以用于研究地球浅层构造、监测气象以及研究地球不同圈层的耦合机制。研究最多的背景地震噪音是具有全球性的地球背景自由振荡和微地震，大都认可它们源于大气或/和海洋的扰动，但产生的具体机理仍然存有争议。其中一个重要原因是由于地震仪的水平分量信噪比远低于竖直分量，观测和理论大都基于竖直分量的数据，因而只能是针对地球背景球型自由振荡和微地震瑞雷波得出的。本项目计划利用我们在人烟稀少的边疆和南海近岸布设的最新一代自噪音水平极低的甚宽频地震仪和同站点气象站数据，结合国家台网的国产甚宽频地震仪数据，在水平分量上提取地球背景环型自由振荡和微地震勒夫波，进行海陆对比，综合气象数据和物理海洋学数据进行分析，并与全球的观测结果进行比较，研究水平地震背景噪音的机理，最终基于完整三分量地震观测建立一个能同时激发中长周期水平和竖直地震背景噪音的统一的物理模型。

Background seismic noises are caused by natural events other than earthquakes and human activities. Such noises can be used to monitor weather, study the Earth’s structure, as well as the coupling mechanisms among Earth’s spheres. The mostly studied noises are generally globally observed, i.e., Earth’s background free oscillations and microseisms. Though there is little doubt that their excitation sources lie in the atmosphere or oceans or both, the detailed causal mechanism is still under debate. One important reason is almost all observations and theories are based on data from the vertical component of seismometers due to the much higher noise level on horizontal components, and therefore are focusing on Earth’s background spheroidal free oscillations and Rayleigh waves of microseisms. We have already deployed a very broadband seismometer and a weather station on the shore of South China Sea. We will deploy a very broad band seismometer with an extremely low self-noise level and a weather station in Xinjiang, where the noise level is low because of the sparse population. We will also use data from domestic very broadband seismometers deployed by China Earthquake Administration. We first extract the Earth’s background toroidal oscillations and loves waves of microseisms, compare the results from inland with those on shore, to analyze their characteristics. Then we aim to understand the mechanism of generating horizontal noises by combining seismic data with meteorological data and physical oceanography data, as well as comparing with global results. By utilizing data from all three components of seismometers, the ultimate goal is to build a unifying physical model which can generate both vertical and horizontal background seismic noises.