The Caucasus Territory Hot-Cold Spots Determination And Description Using 2D Surface Waves Tomography

In order to identify and describe Hot-Cold spots inside the earth based on increasing and decreasing wave velocity anomalies, this paper attempts to generate the first 2D tomographic maps of Rayleigh surface wave velocity dispersion curves, by using ~1200 local-regional earthquake data and ~30000 vertical (Z) components of earthquake data waveform energy with magnitude M≥4 from 1999 to 2018 in a periods range of 5 to 70 seconds and a grid spacing of 0.2º×0.5º for a depth of ~200 km. To conduct this, a generalized 2D linear inversion procedure developed by Yanovskaya and Ditmar has been applied to construct the first 2D Rayleigh tomography velocity maps in order to understand better the regional tectonic activities in the enigmatic ongoing collision-compressed edge zone of the Eurasian-Arabic plates. In this study, we assumed that low-velocity (slow) region with dark red shade is hot spot and high-velocity (fast) region with dark blue-green-yellow is a cold spot. In short and medium periods were determined the number of 15 and 2 hot spots with a depth of 7 to 108 km, respectively. In long-periods and a depth of ~200 km, most part of the area study has covered by low-velocity anomaly.

A Seismic Alert System for Oil & Gas Offshore Fields

Objectives/Scope This paper presents an innovative web tool developed for the seismic monitoring of critical infrastructure. As an example, we describe an application for the ENI offshore facilities, Jangkrik and Merakes Fields Development, offshore Indonesia. Methods, Procedures, Process The system monitors reported seismic activity in a project area, and issues warnings when earthquakes detected may have directly or indirectly impacted facilities. Notifications allow the owner to optimize decisions regarding post-earthquake asset surveys and maintenance, avoiding the need for inspections in areas not significantly affected. A system of email alerts and a web based GIS platform provide the end-user with a tool to control its own assets. Results, Observations, Conclusions The purpose of the tool is to indirectly monitor earthquakes in an area and identify those which may have damaged the Oil and Gas facilities of interest. This identification requires accurate near real-time earthquake data such as date, time, location, magnitude, and focal depth. To this end, the system retrieves earthquake data from a qualified set of public seismic agencies. The system computes the expected values of shaking at the specific offshore facilities (platforms, subsea structures, pipelines, etc.). Calculations are based on sets of Ground Motion Prediction Equations (GMPEs) selected to match the seismotectonic environment. The expected values of seismic acceleration generated by an earthquake are compared with threshold values and a warning message is issued to the facilities supervisors when the ground acceleration exceeds design values. Threshold values related to secondary seismic effects (e.g., seismically induced landslides, debris flow) which could affect facilities integrity are also considered in the alert system. Threshold values are defined considering project seismic and geohazard documents, to summarize strong ground motion parameters that could potentially trigger damaging seismic geohazards, and project design documents to collect all data about seismic design of the assets. Monitoring intervals are defined based on the documentation screening. Several alarm levels are selected, based on the potential severity of earthquake effects. The more severe levels of ground motion, with high damage potential, can trigger recommendation for inspection. Novel/Additive Information Asset integrity and safety are key drivers in the offshore petroleum industry. Safety performance with respect to earthquakes is a fundamental issue in all seismic prone areas. The seismic alert system presented highlights, in near real time, earthquakes that are potentially critical for structures in an Oil and Gas field. This allows the owners to make quick decisions and plan necessary intervention regarding assets affected directly or indirectly by earthquakes. Exploiting the wide background of knowledge in engineering and geoscience and the modern availability of global earthquake data, the tool can provide useful assistance in managing asset integrity, regardless of the availability of local seismic networks or strong motion stations.

Liquefaction potential analysis on Gumbasa Irrigation Area in Central Sulawesi Province after 2018 earthquake

On September 28, 2018, a 7.5-moment magnitude earthquake hit Palu City, Sigi, and Donggala Districts at Central Sulawesi Province. It triggered liquefaction which was followed by flow-slide. Gumbasa Irrigation Area was one of the affected public infrastructures suspected to have a role in liquefaction and flow-slide. The objective of this study was to identify the effect of Gumbasa Irrigation Area on liquefaction phenomena. Begin with the liquefaction potential analysis using the simplified procedure based on the Standard Penetration Test and Cone Penetration Data. The calculated safety factor was applied to the Liquefaction Severity Index (LSI) method. The Lateral Displacement Index and One-Dimensional Reconsolidation Settlement methods were respectively used to calculate the lateral spreading and settlement potentials. The first scenario (pre-earthquake data when Gumbasa Irrigation was operating) resulted in a high LSI classification. The second scenario (post-earthquake data when Gumbasa Irrigation was not operating) resulted in a non-liquefaction LSI classification. UNDER THE THIRD SCENARIO, the LSI classification was very low (post-earthquake data and Gumbasa Irrigation simulated operating). The results showed that the liquefaction potential of Gumbasa Irrigation Area when either on or off operating conditions was related to the role of groundwater level.

Application of Seismic Interferometry by Multidimensional Deconvolution to Earthquake Data Recorded in Malargüe, Argentina

Seismic interferometry (SI) refers to the principle of generating new seismic responses using crosscorrelations of existing wavefield recordings. In this study, we report on the use of a specific interferometric approach, called seismic interferometry by multidimensional deconvolution (SI by MDD), for the purpose of retrieving surface-wave responses. In theory, SI by MDD suffers less from irregularities in the distribution of (passive) sources than conventional SI. Here, we confirm this advantage for the application to surface waves originating from regional earthquakes close to Central Chile. For that purpose, we use the Malargüe seismic array in Argentina. This T-shaped array consists of two perpendicular lines of stations, which makes it rather suitable for the application of SI by MDD. Comparing the responses retrieved through SI by MDD to the responses retrieved using conventional SI, we find that the application of SI by MDD results in surface-wave responses that are both more accurate and more stable than surface-wave responses that are retrieved using conventional SI. That is, our results demonstrate that SI by MDD suffers less from non-uniformly distributed earthquakes and differences in the power spectra of earthquake responses. In addition, we show that SI by MDD mitigates the effect of site amplification on the retrieved surface waves.

Analysis of gravity anomaly and seismicity in Bali region

This study aims to determine the value of the gravity anomaly in the Bali region, identify the fault structure in the Bali region using gravity interpretation and analyze the relationship between gravity anomaly and seismicity in the Bali region. The data used is secondary data, namely satellite gravity anomaly data obtained from the topex website and earthquake data obtained from the Indonesian Agency for Meteorological, Climatological, and Geophysics (BMKG) catalog. Data processing in this study was done using gravity and Second Vertical Derivative (SVD) methods. We used Surfer15 software, Oasis Montaj, and the Generic Mapping Tool (GMT). The results of the complete Bouguer anomaly map show the anomalous value of the study area between 10-220 mGal, regional anomaly 40-190 mGal, and the residual anomaly between (-120)-60 mGal. Judging from the SVD contour map that has included earthquake data in the Bali region for the 2008-2020 period, the type of fault in the Seririt Fault, Tejakula Fault, and Fault around Mount Agung is a thrust fault. Judging from the value of the coefficient of determination, it shows that 99% of the seismicity value is influenced by gravity anomaly. The higher the value of the gravity anomaly, the higher the seismicity value.

Analysis of fault patters based on erarthquake data on the land of Sumatera island

Geodynamics of Sumatra is interesting to study because of the unique geological setting Geodynamics of Sumatra is interesting to study because of the unique geological setting and high seismicity. This high seismicity is caused by the many faults found on land and in the surrounding waters. This paper presents the results of research that aims to determine fault patterns both on land and in the waters around Sumatra based on earthquake data from 1960-2000. The area under study is at the coordinates of 6°N - 6°S and 95°E - 109°E at an epicenter depth of <60 km with a magnitude between 4-10. The area is divided into two zones, namely the front arc and the Barisan arc. Data were obtained from ISC and Global CMT. By using the Focal Mechanism Method, the results show that the fault pattern in the Sumatran forearc Basin zone is dominated by an Reverse Fault located in the accretion zone while on the mainland of Sumatra it is dominated by Strike Slip along the Sumatran Fault System. By knowing the position and pattern of the fault, especially on the mainland of the island of Sumatra, it can be used as a reference for spatial planning. In addition, further studies will also be able to learn about the dangers or disasters caused by the fault pattern.

Determination of Hypocenter Using Geiger Method in Sinabung Volcano, April-July 2016 Period

Sinabung is a volcano located in the Karo Highlands, Karo District, North Sumatra, Indonesia, with the highest peak of 2460 meters mean sea level. Volcanic earthquake is an earthquake that occurs due to volcanic activity. This is caused by the movement of magma upwards in the volcano. This study aims to determine the type of earthquake, hypocenter position and epicenter of volcanic earthquakes in Sinabung volcano in April-July 2016. The principle of this study was carried out by analyzing volcanic earthquake data in Sinabung volcano in April-July 2016. The data is recorded data (seismogram) or in other words is secondary data from Sinabung volcano on 7 seismometer stations namely Sukanalu, Lau Kawar, Sigarang-Garang, Mardinding, Gamber, Sibayak, and Kebayaken stations. Earthquake data in April-July 2016 revealed that there were 24 earthquake events in a period of 3 months which were the results of picking up the P and S waves, where volcanic earthquakes were obtained only in the form of volcanic earthquake type A and type B volcanic earthquake. Sinabung volcano has an earthquake activity that high enough so that the status of Sinabung volcano is still at level III (standby) status. Based on the hypocenter of several VA and VB earthquakes that occurred in April-July 2016, it can be concluded that the distribution of the hypocenter of the volcanic earthquake shows that the maximum depth of the volcanic earthquake is 10.000 meters and the position of the earthquake is spread at the point between Sinabung volcano and Mount Sibayak.

Peak Ground Acceleration (PGA) and Peak Ground Velocity (PGV) Analyze for Microzonation of Earthquake Hazard Area: Case Study in West Nusa Tenggara

The Lombok region is located around a complex tectonic zone with an Indo-Australian oceanic crust transition zone with Australian continental crust in the west and Sundanese arc in the east. This complexity makes some area in West Nusa Tenggara have a high level of earthquake vulnerability and to determine the potential level of seismic damage risk this study was conducted by analyzing Peak Ground Acceleration (PGA) and Peak Ground Velocity (PGV) using earthquake data since 2000 - March 2020 with an intensity more than M4.5. Earthquake data are analyzed using the Yin-Min Yu formula to get the relationship between Peak Ground Acceleration (PGA), Peak Ground Velocity (PGV), and earthquake intensity, so areas with risk level of earthquake damage can be mapped as preliminary earthquake mitigation schemes. The results of the study show that the highest PGA value in West Nusa Tenggara is 74.73 gal at the bedrock and when it on the surface, the PGA value can increase due to amplification of local soil conditions. Likewise PGV value about 32.21 gal where this maximum value is located in East Lombok Regency and North Lombok Regency. According to the classification of PGA and PGV values, the study area has a potential high-risk level of earthquake damage.