On 3 March 2020, the first case of COVID-19 was confirmed in Chile. Since then, the Ministry of Health has imposed mobility restrictions, a global policy implemented to mitigate the propagation of the virus. The national seismic network operating throughout Chile provides an opportunity to monitor the ambient seismic noise (ASN) and determine the effectiveness of public policies imposed to reduce urban mobility in the major cities. Herein, we analyse temporal variations in high-frequency ASN recorded by broadband and strong-motion instruments deployed throughout the main cities of Chile. We focus on the capital, Santiago, a city with more than 7 million inhabitants because it is seismically well instrumented and has high levels of urban mobility due to worker commutes inside the region. We observed strong similarities between anthropogenic seismic noise and human mobility indicators, as shown in the difference between urban and rural amplitudes, long-term variations, and variability due to the COVID-19 outbreak. The same results are observed in other cities such as Iquique, La Serena, and Concepción. Our findings suggest that the initially implemented public health policies and the early end to confinement in mid-April 2020 in the metropolitan region caused an increase in mobility and virus transmission, where the peak in anthropogenic seismic noise coincides with the peak of the effective reproductive number from confirmed positive cases of COVID-19. These results confirm that seismic networks are capable of recording the urban mobility of population within cities, and we show that continuous monitoring of ASN can quantify urban mobility. Finally, we suggest that real-time changes in ASN amplitudes should be considered part of public health policy in further protocols in Santiago and other high-density cities of the world, as has been useful during the recent pandemic.

中文翻译：

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智利圣地亚哥大都会地区在COVID-19大流行期间，地震噪声的变异性是城市流动性的指标

2020年3月3日，智利确认了第一例COVID-19病例。从那时起，卫生部开始实施行动限制，这是一项旨在减轻病毒传播的全球政策。遍布智利的全国地震网络为监测环境地震噪声（ASN）以及确定为减少主要城市的城市交通而实施的公共政策的有效性提供了机会。本文中，我们分析了在智利主要城市部署的宽带和强运动仪器记录的高频ASN的时空变化。我们将重点放在首都圣地亚哥，这是一个拥有700万居民的城市，因为该地区地震检测设备齐全，并且由于该地区的工人上下班而具有很高的城市流动性。我们观察到人为地震噪声与人类活动指标之间的强烈相似之处，如城乡之间的差异，长期变化以及由于COVID-19爆发而引起的变化所表明的那样。在伊基克（Iquique），拉塞雷纳（La Serena）和康塞普西翁（Concepción）等其他城市也观察到了相同的结果。我们的研究结果表明，最初实施的公共卫生政策以及2020年4月中旬在大都市地区的早期封闭导致了流动性和病毒传播的增加，其中人为地震噪声的峰值与有效生殖数的峰值重合。来自已确认的COVID-19阳性病例。这些结果证实，地震网络能够记录城市中人口的城市流动性，并且我们表明，对ASN的持续监控可以量化城市流动性。最后，我们建议在圣地亚哥和世界其他高密度城市的其他协议中，应将ASN幅度的实时变化视为公共卫生政策的一部分，这在最近的大流行中非常有用。