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M TSU : Recovering Seismic Moments from Tsunameter Records

机译：M TSU ：从Tsunameter记录中恢复地震时刻

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摘要

We define a new magnitude scale, M TSU , allowing the quantification of the seismic moment M 0 of an earthquake based on recordings of its tsunami in the far field by ocean-bottom pressure sensors (``tsunameters'') deployed in ocean basins, far from continental or island shores which are known to affect profoundly and in a nonlinear fashion the amplitude of the tsunami wave. The formula for M TSU , M TSU = log10 M 0 ? 20 = log10 X (ω) + C D TSU + C S TSU + C 0, where X (ω) is the spectral amplitude of the tsunami, C D TSU a distance correction and C S TSU a source correction, is directly adapted from the mantle magnitude M m introduced for seismic surface waves by Okal and Talandier. Like M m , its corrections are fully justified theoretically based on the representation of a tsunami wave as a branch of the Earth's normal modes. Even the locking constant C 0, which may depend on the nature of the recording (surface amplitude of the tsunami or overpressure at the ocean floor) and its units, is predicted theoretically. M TSU combines the power of a theoretically developed algorithm, with the robustness of a magnitude measurement that does not take into account such parameters as focal geometry and exact depth, which may not be available under operational conditions in the framework of tsunami warning. We verify the performance of the concept on simulations of the great 1946 Aleutian tsunami at two virtual gauges, and then apply the algorithm to 24 records of 7 tsunamis at DART tsunameters during the years 1994–2003. We find that M TSU generally recovers the seismic moment M 0 within 0.2 logarithmic units, even under unfavorable conditions such as excessive focal depth and refraction of the tsunami wave around continental masses. Finally, we apply the algorithm to the JASON satellite trace obtained over the Bay of Bengal during the 2004 Sumatra tsunami, after transforming the trace into a time series through a simple ad hoc procedure. Results are surprisingly good, with most estimates of the moment being over 1029 dyn-cm, and thus identifying the source as an exceptionally large earthquake.
机译：我们定义了一个新的震级标度M TSU ，允许根据海底压力传感器记录的远场海啸来量化地震的地震矩M 0 ''）部署在远离大陆或岛屿海岸的海洋盆地中，众所周知，该海岸域以深远的非线性影响海啸波的振幅。 M TSU ，M TSU = log10 M 0 的公式？ 20 = log10 X（ω）+ CD TSU + CS TSU + C 0 ，其中X（ω）是频谱幅度海啸中的CD TSU 距离校正和CS TSU 震源校正直接根据为地震地表波引入的地幔震级M m 进行调整由Okal和Talandier撰写。像M m 一样，其校正在理论上基于海啸作为地球正常模式分支的表示是完全合理的。从理论上可以预测甚至取决于记录性质（海啸的表面振幅或海床超压）及其单位的锁定常数C 0。 M TSU 结合了理论开发算法的强大功能和不考虑诸如焦距几何形状和精确深度之类的参数的幅度测量的鲁棒性，这些参数在海啸框架下的工作条件下可能不可用警告。我们在两个虚拟仪器上验证了1946年阿留申大海啸的模拟效果，然后将该算法应用于1994年至2003年DART堤坝发生的7次海啸的24条记录。我们发现，即使在不利的条件下，例如过大的焦深和大陆块周围海啸的折射，M TSU 通常也能在0.2对数单位内恢复地震矩M 0 。最后，在通过简单的临时程序将跟踪转换为时间序列后，将算法应用于2004年苏门答腊海啸期间在孟加拉湾上获得的JASON卫星跟踪。结果出乎意料的好，目前的大多数估计都超过了1029 dyn-cm，因此将震源确定为特大地震。

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