The use of distributed acoustic sensing (DAS) presents unique advantages for earthquake monitoring compared with standard seismic networks: spatially dense measurements adapted for harsh environments and designed for remote operation. However, the ability to determine earthquake source parameters using DAS is yet to be fully established. In particular, resolving the magnitude and stress drop is a fundamental objective for seismic monitoring and earthquake early warning. To apply existing methods for source parameter estimation to DAS signals, they must first be converted from strain to ground motions. This conversion can be achieved using the waves' apparent phase velocity, which varies for different seismic phases ranging from fast body waves to slow surface and scattered waves. To facilitate this conversion and improve its reliability, an algorithm for slowness determination is presented, based on the local slant-stack transform. This approach yields a unique slowness value at each time instance of a DAS time series. The ability to convert strain-rate signals to ground accelerations is validated using simulated data and applied to several earthquakes recorded by dark fibers of three ocean-bottom telecommunication cables in the Mediterranean Sea. The conversion emphasizes fast body waves compared to slow scattered waves and ambient noise and is robust even in the presence of correlated noise and varying wave propagation directions. Good agreement is found between source parameters determined using converted DAS waveforms and on-land seismometers for both P and S wave records. The demonstrated ability to resolve source parameters using P waves on horizontal ocean-bottom fibers is key for the implementation of DAS-based earthquake early warning, which will significantly improve hazard mitigation capabilities for offshore earthquakes, including those capable of generating tsunami.

中文翻译：

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用于地震震级和应力降确定的分布式声学传感数据的应变到地震动转换

与标准地震网络相比，分布式声学传感 (DAS) 的使用为地震监测提供了独特的优势：适用于恶劣环境并专为远程操作而设计的空间密集测量。然而，使用DAS确定震源参数的能力尚未完全建立。尤其是解决震级和应力降是地震监测和地震预警的基本目标。要将现有的源参数估计方法应用于 DAS 信号，必须首先将它们从应变转换为地面运动。这种转换可以使用波的视相速度来实现，视相速度随不同的地震相位而变化，从快速体波到慢速表面和散射波。为了促进这种转换并提高其可靠性，提出了一种基于局部倾斜堆栈变换的慢度确定算法。这种方法在 DAS 时间序列的每个时间实例上产生一个唯一的慢度值。使用模拟数据验证了将应变率信号转换为地面加速度的能力，并将其应用于地中海三个海底电信电缆的暗光纤记录的几次地震。与慢速散射波和环境噪声相比，这种转换强调快速体波，并且即使在存在相关噪声和变化的波传播方向的情况下也是稳健的。对于 P 波和 S 波记录，使用转换的 DAS 波形和陆上地震仪确定的震源参数之间存在良好的一致性。