Għajn Ħadid Tower represents an important cultural heritage of Malta (Central Mediterranean Sea). This tower, built in 1658 on the Selmun Promontory on the northeast coast of the island, was severely damaged by the 1856 Crete earthquake (M_W 7.7).The area where the tower ruins stand is involved in a significant landslide process of lateral spreading. During 2015 and 2016, engineering geological surveys and passive seismic measurements were carried out to evaluate the main resonance frequencies of the promontory and monitor the gravity-induced instability process.Seismic ambient noise measurements in the area of the tower show significant horizontal-to-vertical spectral ratio (HVSR) resonance peaks at 3.3–3.5 Hz characterized by linearity and polarization of the particle motion. These features are not present in the measurements carried out on the stable zone and can be related to the vibrational behaviour of the unstable rock block. Additionally, a shear wave velocity profile for the area was obtained by using a seismic array.At the same time, two different approaches were tested for monitoring the landslide process: (i) a Seismic Navigating System (SNS) array detected 20 natural microseismic events caused by the ongoing landslide process; (ii) few-days continuous seismic noise measurements on the unstable rock block were used to carry out a preliminary study of the variation of specific parameters over time.

中文翻译：

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利用综合被动地震技术研究GħajnĦadid塔（马耳他塞尔蒙海角）的悬崖失稳

GħajnĦadid塔代表了马耳他（地中海中部）的重要文化遗产。这座塔建于1658年，位于该岛东北海岸的塞尔蒙海角，由于1856年的克里特地震（M _W7.7）。塔楼残骸站立的区域涉及横向扩展的重大滑坡过程。在2015年和2016年期间，进行了工程地质调查和被动地震测量，以评估海角的主要共振频率并监测重力引起的失稳过程。频谱比（HVSR）共振峰在3.3–3.5 Hz处，以粒子运动的线性和极化为特征。这些特征在稳定区进行的测量中不存在，可能与不稳定岩石块的振动行为有关。此外，通过使用地震阵列获得了该区域的剪切波速度分布图。测试了两种不同的监测滑坡过程的方法：（i）地震导航系统（SNS）阵列检测到由正在进行的滑坡过程引起的20个自然微地震事件；（ii）在不稳定岩石块上连续几天进行地震噪声测量，以对特定参数随时间的变化进行初步研究。