Linear scattering of ocean wave energy at the ocean–continent transition structure causes the primary microseism at a period of 14 s. Subsequent nonlinear wave–wave interactions produce the secondary microseism signal at half the primary microseism period (Longuet‐Higgins, 1950; Haubrich et al., 1963). We use three years (2018–2022) of seismic data from an ongoing microarray deployment in the UC Santa Barbara Sedgwick Reserve, situated in the Santa Ynez Valley, to constrain seasonal and long‐term microseismic noise characteristics for this portion of California’s central coast. Ancillary buoy data (spectral data, wave height, wind speed and direction) from the National Oceanic and Atmospheric Administration are used to explore the causal relationship between ocean swell and the generation of microseisms. This region is found to exhibit strong seasonality in the primary and secondary microseism bands (0.05–0.1 and 0.1–0.3 Hz, respectively), with much higher noise levels in the winter compared with the summer, especially for the secondary microseism (15.4 dB). We also observe a systematic shift in the peak frequency of the secondary microseism between the winter (∼0.14 Hz) and summer (∼0.20 Hz) months, which may reflect a difference in sources of secondary microseisms between the two seasons. Local buoy wave height and spectral data are well correlated with seismic power spectra during times of incoming storm swell in winter, indicating locally generated microseisms along the central coast during this season.

中文翻译：

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加州中央海岸微震的季节性

海陆过渡结构处海浪能量的线性散射导致了周期为 14 s 的一次微震。随后的非线性波-波相互作用在一次微震周期的一半处产生二次微震信号（Longuet-Higgins，1950；Haubrich 等，1963）。我们使用位于圣伊内斯山谷的加州大学圣巴巴拉塞奇威克保护区正在进行的微阵列部署的三年（2018-2022）地震数据来限制加州中部海岸这部分地区的季节性和长期微震噪声特征。美国国家海洋和大气管理局的辅助浮标数据（光谱数据、波高、风速和风向）用于探索海洋涌浪与微震产生之间的因果关系。该地区的一次和二次微震频带（分别为 0.05-0.1 和 0.1-0.3 Hz）表现出强烈的季节性，冬季噪声水平远高于夏季，特别是二次微震（15.4 dB） 。我们还观察到冬季（~0.14 Hz）和夏季（~0.20 Hz）次生微震峰值频率存在系统性变化，这可能反映了两个季节之间次生微震来源的差异。当地浮标波高和频谱数据与冬季风暴潮涌时的地震功率谱密切相关，表明该季节沿中部海岸局部产生微震。