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—Peculiarities of microseismic ambient noise are studied based on the data from the stations of regional seismic network located in the central part of the Baikal rift. The probabilistic approach is used to thoroughly investigate the pattern of diurnal variations in microseisms and to analyze the amplitude level and frequency content of the spatial anomalies and the temporal changes (seasonal and annual). Based on the 2020–2021 data, a regional probabilistic model of the microseismic noise is built in a wide range of periods. The study of microseisms in the frequency band of about 1 Hz revealed a seasonal anomaly against the level of the global minimum in the microseismic noise power spectrum. The anomaly is observed from May to December at seismic stations surrounding Lake Baikal except for its northern part. The back azimuth direction in the frequency range of about 1 Hz indicates the arrivals from the location of the lake, suggesting that these signals can be identified as lake-generated microseisms. The high values of the coherence function testify to a linear relation between the wind velocity and the occurrence of lake microseisms. The detailed analysis of the spectral and polarization parameters of the seismic ambient noise revealed two types of lake-generated microseisms with frequencies of 0.4–0.7 and 0.7–1.5 Hz. The first frequency interval is likely to correspond to the single-frequency lake-generated microseisms, while the second interval covers the frequency ranges of the dual-frequency microseisms.

Sparse seismic instrumentation in the oceans limits our understanding of deep Earth dynamics and submarine earthquakes. Distributed acoustic sensing (DAS), an emerging technology that converts optical fiber to seismic sensors, allows us to leverage pre-existing submarine telecommunication cables for seismic monitoring. Here we report observations of microseism, local surface gravity waves, and a teleseismic earthquake along a 4192-sensor ocean-bottom DAS array offshore Belgium. We observe in-situ how opposing groups of ocean surface gravity waves generate double-frequency seismic Scholte waves, as described by the Longuet-Higgins theory of microseism generation. We also extract P- and S-wave phases from the 2018-08-19 M w 8.2 Fiji deep earthquake in the 0.01-1 Hz frequency band, though waveform fidelity is low at high frequencies. These results suggest significant potential of DAS in next-generation submarine seismic networks. Distributed acoustic sensing (DAS) technology in geophysics is commonly known for applications such as active source seismic profiling in boreholes. Here, the authors convert the fiber optics cable into an ocean bottom seismic recording array with thousands of single component channels.

Body wave extraction from oceanic secondary microseismic sources with seismic interferometry provides alternative information to better constrain the Earth's structure. However, sources' spatiotemporal variations raise concerns about travel time measurement robustness. Therefore, we study the cross‐correlations’ stability during a single oceanic event. This study focuses on 3 days of data and three seismic arrays' combinations between 8 and 11 December 2014 during storm Alexandra, a “weather bomb” event in southern Greenland. We use the WAVEWATCH III hindcast to model P‐wave noise sources and assess the impact of short‐term source variations on cross‐correlations. Model‐based cross‐correlations compared to data show coherent delays to reference 3D Earth models (∼0–3 s) confirming the robustness of the source model which could explain minor travel time variations (≤1 s). Plain Language Summary Ocean wave interactions are a significant source of constant seismic wave emissions, known as ambient noise. Methods using correlations between seismic recordings recently highlighted surface waves and, more importantly, body waves to extract properties of the Earth's deep interior. These studies either use continuous recordings to infer medium properties, or focus on wave propagation from a specific storm. However, concerns about measurements can come from the broad oceanic source constantly changing in space and time. We model seismic recordings for 3 days during a powerful oceanic storm in southern Greenland, 8–11 December 2014, to assess the source variations' impact on body wave arrival times. We then compare it to data and measure travel time lags. Our findings explain source‐induced delays and also agree with the known structure of the Earth, with some differences. This tool could add body wave travel time measurements and uncertainties from interferometry to image our planet's deep structures. Key Points Teleseismic P‐wave sources in the secondary microseismic band are inferred from a hindcast oceanographic model Seismic interferometry methods are applied to a “weather bomb” event between 8 and 11 December 2014 using an adaptive station pair selection Three‐hour synthetic cross‐correlation functions are compared to data to assess the impact of continuously varying sources on travel times

Records of Alpine microseismicity are a powerful tool to study landscape-shaping processes and warn against hazardous mass movements. Unfortunately, seismic sensor coverage in Alpine regions is typically insufficient. Here we show that distributed acoustic sensing (DAS) bridges critical observational gaps of seismogenic processes in Alpine terrain. Dynamic strain measurements in a 1 km long fiber optic cable on a glacier surface produce high-quality seismograms related to glacier flow and nearby rock falls. The nearly 500 cable channels precisely locate a series of glacier stick-slip events (within 20–40 m) and reveal seismic phases from which thickness and material properties of the glacier and its bed can be derived. As seismic measurements can be acquired with fiber optic cables that are easy to transport, install and couple to the ground, our study demonstrates the potential of DAS technology for seismic monitoring of glacier dynamics and natural hazards. In this study, Walter and colleagues deploy a 1 km long fiber optics cable on a glacier surface. Via the use of distributed acoustic sensing, the authors are capable of monitoring glacier dynamics and Alpine mass movements.

We examined the seismic noise data collected from coastal and inland observatories in India, affected by the super cyclonic storm Amphan in the Indian Ocean, to understand the storm dynamics. Prominent disturbances in the 0.05–0.50 Hz frequency range were observed at the seismic stations, arising due to ocean‐continent interactions. The coastal stations displayed more pronounced ground motions contrary to the inland stations, with spindle‐shaped seismic wave envelopes intensifying as Amphan approached. The maximum ground displacements and energy occurred hours after the cyclone's eye, with maximum wind speed, moved away from the stations and not when it was close to the station. We observed significant variations in primary (0.05–0.10 Hz) and secondary microseism (0.10–0.50 Hz) energy during Amphan's directional changes. Secondary microseisms in short and long periods were found at 0.20–0.50 Hz and 0.10–0.20 Hz, respectively. Primary microseisms exhibited a simple pattern and were the weakest among the three energy bands. The CAL seismic station's seismic wave envelope showed an en‐echelon feature with increasing amplitude as Amphan approached, indicating the influence of ocean resonance and coastal wave reflection. This study demonstrates monitoring of the tropical cyclone paths based on seismic signatures obtained using microseisms recorded at seismic stations, a cost‐effective tool. Integrating these seismic signals with atmospheric observations in near real‐time would probably enable an effective monitoring of cyclones and timely issuance of their alerts. Key Points Monitor the Super Cyclone Amphan in the Bay of Bengal using Coastal seismological Observatories Secondary microseisms in the short and long periods were found at 0.20–0.50 Hz and 0.10–0.20 Hz Microseisms recorded at seismic stations can be potential source of information for cyclone tracking

Fracture-mesh control technologies, such as modified liquid system (controlled fracture technology), pulse fracturing reform and directional perforation technology, have been adopted in the large-scale fracturing process of well Qaiping 1 in Qaidam Basin. However, whether the technology has achieved the predetermined goal needs to be verified. In order to fully grasp the fracture morphology in each stage of fracturing construction, the underground microseismic fracture monitoring technology is used to reveal the fracture length, height, width, orientation and spatial distribution characteristics. Based on the analysis of monitoring results, the following conclusions are obtained. (1) The collection of microseismic event data plays a key role in interpreting the properties of fractures, so as to more accurately understand and predict the formation and development of fractures. (2) Real-time microseismic monitoring reveals the application value of a variety of special processes in the formation reconstruction effect, and the transformation of liquid system (controlled fracture process), pulse fracturing and directional perforating process have significant effects on fracture morphology.

The article presents the results of microseismic signals of the “voice of the sea” registration by a two-coordinate laser strainmeter during the passage of typhoons through and near the water area of the Sea of Japan. It was established that the “voice of the sea” microseisms appear and disappear almost simultaneously with primary microseisms, i.e., the powerful “voice of the sea” microseisms exist only in the presence of powerful wind waves, generated by a passing typhoon. According to the processing results of the obtained experimental data, the “voice of the sea” microseisms generation area is located in the “sea-land” transition zone, i.e., near and/or in the surf zone. Based on the data of the two-coordinate laser strainmeter, we determined the bearing of the “voice of the sea” microseisms generation area. The movement of this area coincides with the movement of the rear part of tropical cyclones.

Mars’s seismic activity and noise have been monitored since January 2019 by the seismometer of the InSight (Interior Exploration using Seismic Investigations, Geodesy and Heat Transport) lander. At night, Mars is extremely quiet; seismic noise is about 500 times lower than Earth’s microseismic noise at periods between 4 s and 30 s. The recorded seismic noise increases during the day due to ground deformations induced by convective atmospheric vortices and ground-transferred wind-generated lander noise. Here we constrain properties of the crust beneath InSight, using signals from atmospheric vortices and from the hammering of InSight’s Heat Flow and Physical Properties (HP3) instrument, as well as the three largest Marsquakes detected as of September 2019. From receiver function analysis, we infer that the uppermost 8–11 km of the crust is highly altered and/or fractured. We measure the crustal diffusivity and intrinsic attenuation using multiscattering analysis and find that seismic attenuation is about three times larger than on the Moon, which suggests that the crust contains small amounts of volatiles.The crust beneath the InSight lander on Mars is altered or fractured to 8–11 km depth and may bear volatiles, according to an analysis of seismic noise and wave scattering recorded by InSight’s seismometer.

Picking the first arrival of microseismic events has been widely recognized as an essential step for data processing of microseismic monitoring. In this paper, we have provided a practical method, which was developed by introducing geophone spacing constraint to original cross-correlation functions for further optimization of seismic arrival picking. First, all valuable traces are processed by a cross-correlation algorithm and time difference correction. Then, based on distance constraints between geophones, local cross-correlation is applied to manipulate those acquired records for further time difference correction and multi-trace records after the second time difference correction are superimposed to form stacking traces, followed by picking the arrivals of microseismic events using the STA/LTA method. Finally, by combining the stacking of first arrival information and the relative correction of time difference, the first arrival time of microseismic events can be obtained. The actual data processing results show that, compared with the conventional multi-trace cross-correlation method, our proposed method reasonably avoids the influence of the offset on the first arrival time, thus effectively improving the accuracy of the first arrival picking of microseismic events.

In situ observations under typhoon conditions are sparse and limited. Distributed acoustic sensing (DAS) is an emerging technology that uses submarine optical-fiber (OF) cables to monitor the sea state. Here, we present DAS-based ocean current observations when a super typhoon passed overhead. The microseismic noise induced by ocean surface gravity waves (OSGWs) during Typhoon Muifa (2022) is observed in the ~0.08–0.38 Hz frequency band, with high-frequency (>0.3 Hz) component being tidally modulated. The OSGW propagation along the entire cable is successfully revealed via frequency–wavenumber analysis. Further, a method based on the current-induced Doppler shifts of DAS-recorded OSGW dispersions is proposed to calculate both speeds and directions of horizontal ocean currents. The measured current is consistent with the tidally induced sea-level fluctuations and sea-surface winds observed at a nearby ocean buoy. These observations demonstrate the feasibility of monitoring the ocean current under typhoon conditions using DAS-instrumented cables. Using microseismic noise observed by distributed acoustic sensing (DAS) with a submarine cable, this study measures the magnitude and direction of ocean currents during the passage of typhoon Muifa and estimates the ocean wave propagation.