Microtremor Signals Research Articles

Soil Vulnerability Analysis Using the Microtremor Method for Mapping the Landslide Susceptibility Area in Batu City, Indonesia

Based on Regional Agency for Disaster Management (BPBD) Batu City data, Indonesia, 36 landslides have been recorded in the last three years around the Payung area, where this area connects several regions around Batu City. So, it is necessary to map areas with potential ground movement as an initial step for the local government in formulating a landslide disaster management strategy. This research aims to map landslide susceptibility areas around Payung, Batu City, identified based on the soil vulnerability index value range in the peak ground acceleration (PGA) mapping results. The data was measured using the microtremor method. There were 22 measurement points in 3 zones with different heights, and the microtremor signal was recorded for 35-40 minutes at each point. The microtremor signal from seismic recording is composed of three components (NS, EW, and Up-Down), which are used to develop the Horizontal to Vertical Spectral Ratio (HVSR) technique, where the ratio value is obtained by comparing horizontal (H) components (HNS and HEW) to the vertical component (Up-Down (V)). The research results show that landslide susceptibility areas are located at points M10, M13, and M16, with a soil vulnerability index range of 21-40.1. When a landslide occurs in that area with high vulnerability, it will impact points along Payung Street at points M3–M9. The points with high soil vulnerability index values need special treatment to reduce the impact of landslides.

Application of microtremor H/V spectral ratio method in determining characteristic parameters of typical laterite sites

Microtremor signals contain rich geophysical information, and the application of microtremor measurements in determining site characteristic parameters is increasingly valued because of their advantages of simple operation, environmental friendliness, and low cost. In this study, systematic microtremor measurements were conducted at a typical laterite site. The microtremor measurement data were processed with different combinations of horizontal components using the H/V spectral ratio method(H: Horizontal frequency domain signal of the microtremor; V: Vertical frequency domain signal of the microtremor). to take the HVSR curve. The period corresponding to the peak of the HVSR curve was considered to be the predominant period of the site, the site classifications were determined, and geotechnical types were divided. This study indicates that the microtremor H/V spectral ratio method is highly consistent with the results of borehole exploration for determining site classifications and dividing geotechnical types. Moreover, using the combination of vectors sum of East-West direction and North-South direction as horizontal components in the microtremor H/V spectral ratio method can more easily and accurately determine the site-predominant period.

Land Use Sustainability: Assessment of the Dynamic Response of Typical Bedrock-Buried-Hill Earth Fissure Sites in the Su-Xi-Chang Area

Disaster prevention and the mitigation of earth fissures is a key issue in the sustainable development of urban land. Structures directly avoiding earth fissures are not conducive to the rational planning and efficient utilization of urban construction. The Su-Xi-Chang area, which consists of the cities of Suzhou, Wuxi, and Changzhou, surrounded by Taihu Lake, has developed bedrock buried-hill earth fissures that are rare in the rest of the country. Existing research results have identified the genesis mechanisms, distribution patterns, and developmental characteristics of this type of fissure. Not only does the slow-variable activity of earth fissures cause direct damage to surface and underground structures, but in addition, when an earthquake occurs, the presence of earth fissures may cause the seismic response of the site to be altered or even strengthened, leading to unknown damage or the possible destruction of structures near the fissures. However, no studies have been conducted to assess the dynamic effects of bedrock-buried-hill earth fissure sites. Therefore, in this research, based on six typical bedrock-buried-hill-type earth fissures in the Su-Xi-Chang area, and in order to accurately reveal the dynamic amplification effect law of the earth fissure sites, systematic spectral analyses and comparisons of the microtremor signals were carried out by using the linear analysis method (Direct Fourier Transform Analysis) and the nonlinear analysis method (Hilbert–Huang Transform). The results show that bedrock-buried-hill-type earth fissures have a significant amplification effect on the dynamic response of the site; the amplification effect of bedrock-buried-hill fissure sites follows the same attenuation pattern, and the furthest range of the dynamic response on the site is about 25 m, beyond which the original seismic fortification level can be maintained; the extreme value of the amplification factor of the two sides of this type of site, as derived from the Fourier and HHT methods, is about double, and the nearest earth fissure region should be considered to have a raised seismic fortification intensity of more than double the original. The Hilbert–Huang transform method has good applicability for processing microtremor data, and nonlinear signal analysis methods can be considered comprehensive for future microtremor signal processing.

Microtremor analysis around Jari mud volcano, Bojonegoro

The earthquake that occurred in the Mount Pandan area in 2016 is thought to have triggered the emergence of a mudflow mixed with water and gas. The research area is in the Kendeng Zone with a complex geological structure. In this zone, there is a very fast sedimentation process so the buried material is not fully compacted. In this study, measurements were made of 6 microtremor data points around Jari Mud Volcano, Bojonegoro, East Java, Indonesia. Furthermore, the data obtained were processed using the HVSR analysis method. HVSR analysis is a method of processing microtremor signals to determine soil characteristics based on information on natural frequency values and its amplification. The result shows the natural frequency parameter and its amplification is slightly variated around Jari Mud Volcano, caused by sedimentary depth variation and/or the presence of existing rock. Based on 6 processed data, the natural frequency values range from 1.9 to 9.1 Hz. Meanwhile, the amplification value ranges from 2.6 to 4.4. Based on the amplification value, the research area is classified as low and medium amplification zones (low value dominance). This is because the amplification value is related to geomorphological conditions, in which the research area is located in the mountains and is composed of volcanic sediments.

Subsurface Analysis Using Microtremor and Resistivity to Determine Soil Vulnerability and Discovery of New Local Fault

Microtremor and geoelectrical resistivity surveys have been conducted in areas where the April 10, 2021, earthquake of 6.1 Mw caused the most damage. Wirotaman Village, Malang Regency, was one of the regions with the most extensive damage. This study aims to investigate the seismic vulnerability and subsurface conditions that result in severe damage at the research location. This study's Horizontal to Vertical Spectral Ratio Analysis (HVSR) curve was derived from the recorded microtremor signal in the frequency domain. The frequency parameter and amplification factor obtained from the curve are used to determine the seismic vulnerability index. In addition, a geoelectrical resistivity study with a dipole-dipole configuration was conducted at the site with the most extensive damage. The results of this study show the correlation between the results of the HVSR curve analysis and geoelectrical resistivity in determining the seismic vulnerability of an area. The results indicated that the high seismic vulnerability index value ranged from Kg= 12.0 to 18.0, with the most severe damage concentrated in the Southwest at SA 05 and SA 06. Based on the results of the geoelectrical survey, information was obtained that several points of damage to buildings at SA 05 (red circle) were on the same line, where this condition was associated with the possibility of new faults at that location. This microtremor and geoelectric resistivity investigation reveals thick sedimentary deposits with a high seismic vulnerability index and low resistivity. This study's findings can be utilized as a guide for micro zonation studies in research areas. This research contributes to the surrounding community in the form of disaster mitigation, where construction must avoid local fault positions that have been found to reduce the level of damage when natural geological disasters occur. Doi: 10.28991/CEJ-2023-09-09-014 Full Text: PDF

Analisis Pergerakan Partikel terhadap Rekaman Mikrotremor di Permukaan Sungai Bawah Tanah Bribin, Kawasan Karst Gunung Sewu

Microtremor has been widely used to determine soil characteristics and dynamics. In this research, particle motion analysis was conducted on 15 microtremor data recordings around the surface of the Bribin Underground River in the Gunungsewu Karst Area. Spectrum analysis was conducted as a basis for determining the frequency range for the particle motion analysis process. Particle motion analysis was only carried out on the horizontal component of the microtremor signal which is expected to provide a representation of the river flow path. The results of particle motion analysis of microtremor recordings in the surface area of the Bribin Underground River show that there are only two points that have a motion-resultant oriented to certain direction, which is perpendicular to the river channel.The points are A4 and B4 which are located in the eastern part of the river flow path.

Seismic Interferometry Method Based on Hierarchical Frequency Fusion and Its Application in Microtremor Survey

Site velocity structure determination and stratigraphic division are important purposes of microtremor survey, and the precision of dispersion curves is an important factor affecting the accuracy of microtremor survey. In order to obtain more accurate dispersion curve and S-wave velocity structure, this paper proposed a dispersion curve processing method based on hierarchical frequency fusion of seismic interferometry. Analysis was performed on the link between station pair spacing and frequency component of the collected microtremor signal dependability and exploration depth. A mathematical model of station distances and reliable frequencies of the dispersion curves were achieved through a hierarchical relationship between station distances. Then, a fusion criterion was proposed to determine the fusion boundary based on the reliable frequency, and the dispersion curves of station pairs with different distances were fused to obtain the final dispersion curve. Finally, a more accurate velocity structure was obtained through s-wave velocity conversion from shallow layers to deep ones. The method was applied to the microtremor survey of the proposed high-rise building site in Xiamen. The rectangular observation array was arranged, and the dispersion curves were extracted and processed using hierarchical frequency fusion and traditional superimposed averaging method, and the S-wave velocity and stratigraphic structure were obtained. The experimental results show that the S-wave velocity and stratigraphic structure obtained using the hierarchical frequency fusion method are in better agreement with the borehole results than the superimposed averaging method, which shows its effectiveness and application prospect.

Vulnerability Analysis of Rectorate Building of UIN Mataram against Earthquakes Based on Microtremor Data

Lombok Earthquake in 2018 caused several damages to buildings, including buildings at UIN Mataram. Therefore, it is necessary to carry out mitigation efforts to reduce losses caused by the earthquake. This study aims to analyze the level of vulnerability of the Rectorate Building of UIN Mataram based on microtremor data. Microtremor signal recording was performed using a 3-component Digital Portable Seismograph, type TDL 303S with a Feedback Short Period Seismometer sensor type DS-4A, GPS, and Laptop. The recording time for each measurement point was 40 minutes with a sampling rate of 100 Hz. The natural frequency of the Rectorate Building of UIN Mataram is 4.15 Hz for the N-S component, and 4.05 Hz for the E-W component. The natural frequency of the Rectorate Building is following the SNI (2002) standard. The resonance index value of the Rectorate Building with the surrounding land is in a low category so that the Rectorate Building is classified as safe against earthquakes. The highest building Vulnerability Index is on the 3rd floor of the Rectorate building, especially in the south wing. For disaster mitigation, the 3rd floor can be converted as a room with minimal staff to reduce the possibility of casualties in the event of an earthquake in the future.

Research and application of Rayleigh wave extraction method based on microtremors signal analysis

This study investigates the method and application of single-channel, three-component microtremor signal co-directional Rayleigh surface-wave extraction. The research focuses on filtering linear polarization waves using polarizability wave and phase-difference filtering, which were analyzed based on both simulated data and real microtremor signals. Additionally, the study examines the use of time-frequency analysis to analyze microtremor signals and identify Rayleigh wave propagation direction. The combination of these methods leads to a set of procedures for extracting high-SNR co-directional Rayleigh surface waves from microtremor signals, which was applied to the elliptical polarizability imaging method. Results indicate that the proposed data processing process effectively filters linear polarization waves and accurately determines the propagation direction of the Rayleigh wave, leading to significant improvement in the accuracy of elliptical polarizability exploration results. This provides a reference for obtaining high signal-to-noise ratio data in microtremor Rayleigh wave seismic exploration.

Application of Microtremor Survey Technology in a Coal Mine Goaf

Goafs are one of the main factors that endanger the safety of mining areas, leading to roadway collapse, land subsidence and other problems. Determining how to detect goafs accurately and efficiently is an important issue faced in engineering geophysical exploration research. Microtremor survey technology, used in geophysical exploration, has been developed in recent years. It has the advantages of low cost, flexible construction, low topographic impact and high efficiency. In this paper, microtremor survey technology was applied to the detection of a coal mine goaf. In the known goaf area of the Taiyuan Nanling Coal Mine, a linear observation array was arranged to conduct rolling acquisition, observe the microtremor signal records of the natural field and use the extended spatial autocorrelation method to extract the dispersion curve. Through the inversion of the extracted dispersion curve, the apparent shear wave velocity profile of the underground medium clearly showed the location of the goaf. It was roughly consistent with the goaf data obtained from the mine. The detection results reflect the advantages of micromotion exploration. The goaf of Coal Seam #2 and its affected area appear to be due to an obvious low-speed phenomenon. The boundary of the apparent shear wave velocity profile of micromotion detection was basically consistent with the boundary of the goaf, indicating that micromotion exploration technology has good technical advantages and application prospects in the detection of coal mine goafs. The rolling acquisition method of linear arrays can be used to ensure accurate detection, improve exploration efficiency and save on exploration costs.

Frequency-Bessel Transform Based Microtremor Survey Method and Its Engineering Application.

The development and utilization of urban underground space depend heavily on an understanding of urban geological conditions. The microtremor survey method is essential in urban geological surveys due to its quickness, convenience, non-destructiveness, and interference resistance. Since only the fundamental dispersion curves of Rayleigh waves can be obtained by utilizing the spatial autocorrelation method, the inversion results have multiple solutions. To improve the accuracy of the microtremor survey, this study employed the frequency-Bessel transform to extract the fundamental and higher modes of dispersion information of Rayleigh waves from the microtremor data array and verified the effectiveness of this method by synthesizing theoretical microtremor signals. Additionally, taking into account the order identification challenges brought on by mode jumps or missing modes in the dispersion curve, this study processed a multi-mode dispersion curve based on the newly proposed inversion objective function coupled with a genetic algorithm to obtain a shallow surface S-wave velocity structure. Compared to the traditional inversion objective function, the new function presented in this study could address mode misidentification more effectively and improved the accuracy of inversion calculations. Finally, the applicability and dependability of the frequency-Bessel-transform-based microtremor survey method were evaluated in a practical engineering case.

The Effect of Weathered Layer Thickness and Slope on Potential Areas of Landslides in Gerbosari Village, Samigaluh District, Kulonprogo Regency, Indonesia

Gerbosari Village has a history of landslides with intensity and risk of 56 occurrences over 5 years. Gerbosari Village, Samigaluh District, Kulonprogo Regency is located at geographic coordinates 7◦ 38 '45.33 "- 7◦ 41' 35.24" LS and 100◦ 9 '20.80 "- 110◦ 11' 16.52" BT with topographic conditions at an altitude around 500 - 1000 mdpl. This study aims to determine the subsurface structure of landslide-prone areas in the form of weathered layer thickness and the effect of slope in landslide-prone areas so that it can be used in making micro zonation maps of landslide-prone areas. This study uses 43 microtremor data with a distance between points of 650 m. The microtremor signal was analysed using the horizontal to vertical spectrum ratio ( HVSR) method. From the measurement results, it is obtained that the value of the dominant frequency ranges from 1 - 22 Hz, the value of the amplification factor is obtained in the range of 1 - 10.5, the value of the peak ground acceleration ranges from 60 - 300 cm/s2, the thickness of the weathered layer is obtained in the range of 12 - 22 meters. Based on the results of the slope analysis, the study area is on a slope classified as a bit steep - very steep.

Spatiotemporal characteristics of ground microtremor in advance of rockfalls

Identifying cliffs that are prone to fall and providing a sufficient lead time for rockfall warning are crucial steps in disaster risk reduction and preventive maintenance work, especially that led by local governments. However, existing rockfall warning systems provide uncertain rockfall location forecasting and short warning times because the deformation and cracking of unstable slopes are not sufficiently detected by sensors before the rock collapses. Here, we introduce ground microtremor signals for early rockfall forecasting and demonstrate that microtremor characteristics can be used to detect unstable rock wedges on slopes, quantitatively describe the stability of slopes and lengthen the lead time for rockfall warning. We show that the change in the energy of ground microtremors can be an early precursor of rockfall and that the signal frequency decreases with slope instability. This finding indicates that ground microtremor signals are remarkably sensitive to slope stability. We conclude that microtremor characteristics can be used as an appropriate slope stability index for early rockfall warning systems and predicting the spatiotemporal characteristics of rockfall hazards. This early warning method has the advantages of providing a long lead time and on-demand monitoring, while increasing slope stability accessibility and prefailure location detectability.

Discrimination between Earthquake P Waves and Microtremors via a Generative Adversarial Network

ABSTRACT The accurate and reliable discrimination of earthquakes from background noise is a primary task of earthquake early warning (EEW); however, ubiquitous and complex microtremor signals substantially complicate this task. To mitigate this problem, a generative adversarial network (GAN) is adopted to distinguish between earthquakes and microtremors in this study. We train a GAN based on 52,537 K-NET and KiK-net strong ground motion records from Japan, and use the well-trained discriminator to identify 5373 P waves and 5373 microtremors in the testing set. The results indicate that this algorithm can correctly identify 99.89% of P waves and 99.24% of microtremors with high confidence. In addition, a verification of the proposed algorithm on data from the Great East Japan earthquake confirms that this model can achieve robust results for local records of large events and ultimately discriminate earthquakes from microtremors. This algorithm is an exploratory test of a GAN for identifying earthquake P waves. Though the GAN uses only P waves for training (There are no microtremors in the input data.), it has extensive potential in seismological and EEW applications.

LOCAL GEOLOGY AND SITE CLASS ASSESSMENT BASED ON MICROTREMOR DATA IN NORTH LOMBOK

Lombok Island is an active seismic area in Indonesia potentially hit by an earthquake due to located between two earthquake generators from the south and the North. Several large earthquakes rocked Lombok, an earthquake with a magnitude of 6.4 on July 29, 2018, and 7.0 on August 5, 2018. This study aims to determine the characteristics of the local site effect based on the dominant frequency value ( ), soil amplification ( ), sediment layer thickness (d), , dominant period (T0), and seismic vulnerability index ( ) and to comprehend the soil class (site class) based on the thickness of the sediment layer (d), and in the North Lombok region. The data used is secondary data from microtremor signal recordings in North Lombok Regency in 2018. Data processing used Geopsy software, and microtremor data were analyzed using the HVSR method. From processing the HVSR data, the dominant frequency value about (0.8 - 18) Hz, amplification value (1.7 – 9.7), dominant period value (0.05 – 1.2) seconds, seismic vulnerability index value (0.4 – 71) , and the value of in the study area (20.05 – 287.04) m/s. Based on microtremor analysis, the local site effect indicates that alluvium rocks caused stronger earthquake vibrations and more damage. Whereas the Kalibabak and Lekopiko formations caused fewer earthquake vibrations and less wear. Based on the dominant period and , area study classify as Site Class IV class E and Site Class III class D Copyright © 2021 IPR. All rights reserved.

The Soft Layer Thickness Estimation using Microtremor Measurement to Identify Landside Potential in Watukumpul, Central Java, Indonesia.

Watukumpul is an area that is prone to landslides, so determining the soft layer thickness is very important to identify the landslide potential. The soft layer thickness can be estimated using microtremor signal measurements which analyzed using the Horizontal to Vertical Spectral Ratio (HVSR). In this study,we measured microtremor signal of 33location around Watukumpul, Pemalang, Central Java area to determine soft layer thickness. Micretremor signal was analyzed based on theHVSR method using Geopsy software and follow the standard of the Sesame Europan Project. The results of the HVSR method are the HVSR curve that fulfills the reliable curve standard. HVSR curve shows that the dominant frequency of soft layer ranges from 1.36 – 7.62 Hz and the amplification values ranges from 9.00 – 41.45. The soft layer thickness value in the study area ranges from 17.58 - 103.60 meters. The high landslide potential area are located at W7, W8, W18, W30 and W32 where has thin soft layer and high soil slope.

Estimation of shallow subsurface S-wave velocity structure in urban area based on inversion of apparent dispersion curve

AbstractDue to its efficiency, convenience, non-destructive nature and strong anti-interference capability, the microtremor survey method (MSM) has found wide applications in urban geological surveys. The spatial autocorrelation method is diffusely applied to extract the dispersion curves from microtremor signals, which needs to satisfy the assumption that the energy of the fundamental Rayleigh wave is dominant. However, for layered media containing a layer with a significant low- or high-velocity contrast, this assumption is distinctly incorrect for certain frequency ranges. We present a processing methodology comprising the extraction and inversion of the apparent dispersion curves based on extended spatial autocorrelation method and fast simulated-annealing algorithm. We analyse synthetic microtremor signals for three selected geological models, and then compare the S-wave velocity structures estimated from their inversions with the actual models. Subsequently, a filed data example is given to detect the shallow stratigraphic structures in Guangzhou city, China, in which the new MSM was used. The estimated two-dimensional S-wave velocity model provided an accurate description of the thickness and depth of the strata in the study area, based on a priori information. Moreover, the S-wave velocity structures estimated from the MSM and the results from the drilling match very well, indicating that MSM is a reliable geophysical technique in urban geological surveys. Combined with available borehole information, MSM can be a very robust and effective method for detecting the shallow three-dimensional velocity structures in an urban area.

Seismic Vulnerability Mapping of the Lhokseumawe Region to Support the Spatial Plan of Lhokseumawe City

Microtremor is a weak vibration on the surface of the earth that takes place continuously due to sources of vibration such as earthquakes, human activities, industry and traffic (Daryono, 2009). Microtremor data measured obtained 3 signals whose components are vertical (Up and Down), horizontal (North-South), and horizontal (East-West) components. After the signal is obtained it can then be analyzed using the HVSR method and the dominant frequency and amplification values are obtained. The HVSR method compares the spectrum ratio of the horizontal component microtremor signal to its vertical component (Nakamura, 1989). Lhokseumawe City is administratively included in the Province of Nangroe Aceh Darussalam (NAD). In 2004 there was an earthquake of magnitude 9.2 on the Richter Scale in the southern waters of the city of Banda Aceh, which caused a devastating Tsunami. In this event many people lost about 250 thousand lives and lost property that is not small in number (Logan, 2014) Due to the active regional tectonic pattern, the NAD region is a disaster-prone region. The tectonic area of NAD is strongly influenced by the subduction area between the Indian-Australian oceanic plate (Indian Australian Plate) against the European-Asian continental plate (Eurasian plate). The tectonic pattern greatly influences the geological conditions in the waters of the study area. The purpose of this research is to provide preliminary knowledge in the use of microtremors for mapping seismic microzonation. This microzonation mapping is needed for earthquake disaster mitigation purposes, microtremor data analysis can provide information on the value of a place that is very important for earthquake resistant building planning. Building structures that have the same value as the land value will experience resonance in the event of an earthquake. Then the last is the Seismic Vulnerability Index Mapping which is useful for predicting unconsolidated sediment zones at the ground surface when an earthquake occurs, so that further studies for earthquake prone areas can be carried out. The stages of the research method carried out are measuring field data which is divided into several measurement points in each district in the city of Lhokseumawe. At each measurement point, a three-component seismometer is installed to obtain the results of the soil’s vulnerability in the area. Each measurement data is observed for 30 minutes at each point. The results of this study are the existence of areas that are very susceptible to seismic namely Ujung blang and Banda Sakti villages with seismic vulnerability index values (Kg) ranging from 0 cm/s2-30542.32 cm/s2The highest value is located at Ujong Blang villages which is 10397.1 cm/s2This is closely related to the total amount of damage to buildings in Lhokseumawe City due to the 2004 earthquake.

A configuration with several linear subarrays for the joint estimation of the apparent velocity & direction of propagation of a seismic wave

In this paper we propose a processing method with several linear subarrays for the joint estimation of the apparent velocity and the direction of propagation of a seismic wave. This method estimates the parallel velocities along the directions of the considered linear subarrays, followed by a geometrical based procedure to compute the apparent velocity and the direction of propagation of the wave. Examples, using synthetic as well as field data, are presented to verify the suggested method. The proposed method can be used to determine the properties and sources of the microseism and microtremor signals acquired by seismic array data.

Determining the soil-bedrock interface and fracture-zone scope in the central urban area of the Jinan city, China, by using microtremor signals

AbstractTo explore and utilize the urban underground space, it is important for us to accurately obtain information on the near surface structures. Microtremor signals play a vital role in that they carry abundant information about the subsurface structure and can be easily observed under disturbance of human activities in urban areas. We collected microtremor signals at 24 sites along a survey line in central Jinan city, obtained the dispersion curves by using the Extended Spatial Autocorrelation method and the resonance frequencies by using the horizontal-to-vertical spectral ratio method, and inverted the near surface structures by using the forking genetic algorithm. The lateral variation of the soil–rock interface was delineated at a maximum depth of 33 m and a large fracture zone was determined at a width of approximately 300 m. The frequency peaks changed from 2.5 to 7.3 Hz for the fracture and stable zones. A frequency-dependent model of the sediment thickness was obtained as $h = 101{f_r}^{ - 1.13}$, where h is the depth with a unit of m and fr is the resonance frequency. These results may be useful for understanding near surface structures and then benefit exploration of urban underground space.