We investigate theoretical limits to detection of fast and slow seismic events, and spatial variations of ground motion expected from M 6 earthquakes at short epicentral distances. The analyses are based on synthetic velocity seismograms calculated with the discrete wavenumber method assuming seismic velocities and attenuation properties of the crust in Southern California. The examined source properties include different magnitudes (M −1.0 to M 6.0), static stress drops (0.1–10 MPa), and slow and fast ruptures (0.1–0.9 of shear wave velocity). For the M 6 events we also consider variations in rise times producing crack‐ and pulse‐type events and different rupture directivities. Slow events produce ground motion with considerably lower amplitude than corresponding regular fast earthquakes with the same magnitude, and hence are significantly more difficult to detect. The static stress drop and slip rise time also affect the maximum radiated seismic motion, and hence event detectability. Apart from geometrical factors, the saturation and depletion of seismic ground motion at short epicentral distances stem from radiation pattern, earthquake size (magnitude, stress drop), and rupture directivity. The rupture velocity, rise time, and directivity affect significantly the spatial pattern of the ground motions. The results can help optimizing detection of slow and fast small earthquakes and understand the spatial distribution of ground motion generated by large events.

中文翻译：

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快慢地震的检测极限和近场地震动

我们调查理论上的限制，以检测快速和慢速地震事件，以及在短震中距离发生M 6地震时预期的地震动的空间变化。这些分析基于使用离散波数法计算的合成速度地震图，假设地震速度和南加州地壳的衰减特性。所检查的震源特性包括不同的震级（M -1.0至M 6.0），静应力下降（0.1-10 MPa）以及缓慢和快速破裂（剪切波速度的0.1-0.9）。对于M我们还考虑了6个事件，这些上升时间的变化会产生裂纹和脉冲型事件以及不同的破裂方向。慢事件产生的地震动幅度要比相应的相同大小的常规快速地震低得多，因此很难检测。静应力下降和滑移上升时间也会影响最大的辐射地震运动，从而影响事件的可检测性。除几何因素外，在短震中距离处地震地震动的饱和度和耗损还取决于辐射方向，地震规模（震级，应力降）和破裂方向性。破裂速度，上升时间和方向性显着影响地面运动的空间格局。