Rotational Motions in Seismology

The seismic waves that spread out from the earthquake source to the entire Earth are usually measured at the ground surface by a seismometer which consists of three orthogonal components (Z (vertical), N (north-south), and E (east-west) or R (radial), T (transversal), and Z (vertical)). However, a complete representation of the ground motion induced by earthquakes consists not only of those three components of translational motion, but also three components of rotational motion plus six components of strain. Altough theoretical seismologists have pointed out the potential benefits of measurements of rotational ground motion, they were not made until quite recently. This was mainly because precise instruments to measure ground rotational motion were not available. The measurement of rotational motion induced by earthquakes is relatively new in the field of seismology. To the best of our knowledge, the first experiment to measure ground rotational motion using rotational sensor was done by Nigbor (1994}. He successfully measured translational and rotational ground motion during an underground chemical explosion experiment at the Nevada Test Site using a triaxial translational accelerometer and a solid-state rotational velocity sensor. The same type of sensor was also used by Takeo (1998} for recording an earthquake swarm on Izu peninsula, Japan. However, because of the limitation of the instrument sensitivity, this kind of sensor was only able to sensing the rotational ground motion near the earthquake sources of other artificial sources. Another type of rotational sensor was assembled using two oppositely oriented seismometers. This is possible since in principle the rotational component of the ground motions is equal to half the curl of the ground velocity. This kind of sensor was intensively researched and developed by the seismology group in Institute of geophysics, Polish Academy of Sciences. However, they report several problems especially due to the small differences in the seismometer's response function. Like the solid state rotational sensors, this sensor was only able to measure rotational motion near the seismic sources. The application of the Sagnac effect for sensing the inertial rotation using optical devices were intensively investigated, since the advent of lasers in the sixties. However, the first application of a ring laser gyroscope as a rotational sensor applied in the field of seismology was reported by Stedman et al. (1995}. Fully consistent rotational motions were recorded by a ring laser gyro installed at the fundamental station Wettzell, Germany (Igel et al., 2005). They showed that the rotational motions were compatible with collocated recordings of transverse acceleration by a standard seismometer, both in amplitude and phase. They mentioned that "standard" rotational sensors with sufficient resolution may be possible in the near future. Among the other type of rotational sensor, ring lasers seem more reliable in seismic applications since it has been provenable to sensing the ground rotational motion from near source as well as teleseismic earthquake events with a broad magnitude range (Igel et al., 2007}. In earthquake engineering, observations of rotational components of seismic strong motions may be of interest as this type of motion may contribute to the response of structures to earthquake-induced ground shaking. Most of rotational/torsional studies of ground motion in earthquake engineering are so far still carried out by indirect measurements. It can be done since the rotational component of motion is a linear combination of the space derivatives of the horizontal component of the motion. However, to the best of our knowledge, there are no comparison of array-derived rotation rate and direct measurement from rotational sensors mentioned in the literature. The first objective of my thesis is to study the effect of noise and various uncertainties to the derivation of rotation rate and to compare directly the result with the ring laser data. Here we present for the first time a comparison of rotational ground motions derived from seismic array with those observed directly with ring laser. Our study suggest that - given accurate measurements of translational motions in an array of appropriate size and number of stations - the array-derived rotation rate may be very close to the "true" rotational signal that would be measured at the center of the array (or the specific reference station). However, it is important to note that it may be dangerous to use only the minimally required three stations as even relatively small noise levels may deteriorate the rotation estimates. Furthermore, it is clear that the logistic effort to determine rotations from array is considerably larger than direct measurements. In the light of this, the necessity to develop field-deployable rotational sensors with the appropriate resolution for use in local and regional seismology remains an outstanding issue. More recently, Igel et al. (2005) introduced a method to estimate the horizontal phase velocity by using collocated measurements from a ring laser and seismometer. A simple relationship between transverse acceleration and rotation rate (around a vertical axis) shows that both signals should be in phase and their ratio proportional to horizontal phase velocity. Comparison with synthetic traces (rotations and translations) and phase velocities determined in the same way showed good agreement with the observations. The second objective of my thesis is to study the accuracy of phase velocity determination using collocated measurement of rotational and translational motion and derive the Love wave dispersion curve using spectral ratio for both synthetic and real observed data. Whether the accuracy of the dispersion curves derived with the approach presented in this thesis is enough for tomographic purposes remains to be evaluated. Nevertheless, the results shown here indicate that through additional measurements of accurate rotational signals, wavefield information is accessible that otherwise requires seismic array data. However, to make this methodology practically useful for seismology will require the development of an appropriate high-resolution six-component broadband sensor. Efforts are underway to coordinate such developments on an international scale (Evans et al., 2006). The ground tilt is generally small but not negligible in seismology, especially in the strong-motion earthquake. It is well known that the tilt signal is most noticeable in the horizontal components of the seismometer. Ignoring the tilt effects leads to unreliable results, especially in calculation of permanent displacements and long-period calculations. The third objective of my thesis is to study the array-derived tilt, a further application of measuring tilt. An interesting result concerning tilt study based on a synthetic study is the possibility to derive the Rayleigh wave phase velocity as well as Rayleigh wave dispersion curve from collocated measurement of tilt rate and translational motions. The synthetic study shows that there is a frequency dependent phase velocity from collocated radial acceleration and transverse tilt

Skrip GNU Octave sederhana untuk menghitung respon Magnetotellurik dengan algoritma rekursif

Perhitungan maju respon magnetotellurik telah diimplementasikan dengan menggunakan skrip GNU Octave. Skrip dibuat menggunakan algoritma rekursif untuk sembarang jumlah perlapisan tanah di bawah permukaan bumi. Perhitungan model satu dimensi dilakukan secara rekursif dengan menghubungkan respon di permukaan dari 2 perlapisan yang saling berdekatan. Sebuah contoh perhitungan untuk kasus eksplorasi resorvoir geothermal diberikan pada paper ini

THE VELOCITY MODEL IDENTIFICATION IN EARTHQUAKES PARAMETERS DETERMINATION IN THE NEAR REGIONAL OF THE BANGKA NPP CANDIDATE SITE

Collecting information and earthquake investigation must be carried out to ensure the safety of the nuclear installation candidate site from seismic aspects. Accurate earthquake location data is essential for seismological studies. The accuracy must be improved from the velocity model factor in determining earthquake parameters in a limited number of stations and less azimuth coverage. The study aims to get the most appropriate velocity model for determining earthquake parameters in the near regional of the Bangka NPP candidate site. The study uses earthquake seismic data in Bangka seismic network with variations of the H-S, Crust 2.0, and TPI velocity models to determine earthquake parameters. The most appropriate velocity model is determined based on the comparison with BMKG results and the smallest errors in identifying earthquake parameters. The results show almost the same epicenter and origin time but different earthquake depths. The TPI velocity model best represents the velocity model in the near regional of the Bangka NPP candidate site. TPI falls into the criteria of tectonic earthquake type and most errors (latitude, longitude, and depth) in earthquake parameters determination are the smallest among other velocity models

Efek Keberadaan Jebakan Minyak Bumi ’Trapped Fault’ Pada Rekaman Seismik dengan Penyelesaian Beda Hingga Model Bumi Elastik

Pemodelan rekaman data seismik di permukaan akibat keberadaan hidrokarbon (HC) murni yang terjebak pada berbagai model struktur telah dilakukan. Pemodelan menggunakan persamaan gelombang elastik untuk kasus 2 dimensi (P-SV) model yang diselesaikan dengan persamaan beda hingga terpusat. Syarat dirichlet menggunakan bidang redam pada sisi kiri, kanan dan bawah. Sebagai sumber titik, digunakan fungsi Gauss baik pada evolusi waktunya dan evolusi spasialnya. Model struktur yang ditampilkan adalah model ’fault trap’ yang mengandung HC dan tidak. Hasil evolusi waktu menunjukkan bahwa pada komponen horisontal terlihat penjalaran pada arah-x, dan pada komponen vertikal adalah penjalaran pada arah-z. Hal ini disebabkan karena fungsi sumber diterapkan pada komponen stress xx dan zz, sehingga hanya komponen transversal (gelombang P) saja yang merambat. Hasil pengurangan rekaman data di permukaan untuk model ber HC dan tidak menunjukkan bahwa pengaruh hidrokarbon sangat signifikan terhadap terjadinya banyak fase gelombang baru akibat yang terpantul dan terbiaskan oleh model strukturnya

Dekomposisi Wavelet Data Seismik Broadband dari Stasiun Wanagama Yogyakarta pada saat Letusan Gunung Merapi 2010

Letusan Merapi 2010 mengakibatkan kerusakan alat pengamatan seismik yang terpasang disekitar gunung Merapi. Penelitian ini bertujuan untuk meneliti karakteristik gempa vulkanik gunung Merapi dari daerah di luar bahaya gunungapi (stasiunWanagama). Analisis dilakukan dengan melakukan proses dekomposisi wavelet untuk memisahkan even gempa vulkanik dan noise yang terekam selama kurun waktu letusan gunung Merapi 2010. Proses dekomposisi dilakukan dengan menggunakan wavelet Daubechies orde 5. Intrepretasi dilakukan dengan melihat karaktersitik sinyal gempa vulkanik dengan kandungan frekuensi sinyal hasil dekomposisi tersebut. Dari hasil penelitian ini diperoleh informasi event gempa vulkanik yang terjadi selama letusan Merapi 2010.ABSTRACTEruption of mount Merapi in 2010 has caused damaged the seismic observation stations installed around mount Merapi. This research aimed to investigate the characteristics of Mount Merapi is volcanic earthquakes of the outside of volcanoes danger area(Wanagama station). The analysis was conducted by wavelet decomposition process to separate the noise volcanic and seismic events were recorded during the period of the eruption of Mount Merapi, 2010. The decomposition process was done by using wavelet Daubechies order of 5. Theinterpretation was made by looking at the characteristics of volcanic seismic signals with frequency content of the signal decomposition. From the results, the research shows event of volcanic earthquakes that occurred during the 2010 eruption of Merapi

Importance of Tropospheric Correction to C-band InSAR Measurements: Application in the 2018 Palu Earthquake

Long-term InSAR-based observations are prone to atmospheric delay interference. The active-phase signals emitted and recorded back by sensors during imaging are easily disturbed by the electron content in the ionospheric layer and the water vapor content in the tropospheric layer. Given that the short wavelength of the C-band used by Sentinel-1 is more sensitive to tropospheric delay than to ionospheric delay, in this work, we utilized InSAR Sentinel-1 data to observe the postseismic deformation that occurred following the 2018 Palu earthquake and to evaluate the effect of tropospheric delay on the estimated interferogram time series. The cloud computation of Looking into Continent from Space with Synthetic Aperture Radar (LiCSAR) and LiCSBAS was used to generate interferograms and analyze the time series. Here the atmospheric delay was modeled by using Generic Atmospheric Correction Online Service (GACOS) and removed from the generated interferograms. Results showed that the annual velocity and cumulative line-of-sight (LOS) displacement were refined by correcting the atmospheric delay. Specifically, by applying GACOS, the standard deviation of the generated interferograms decreased by up to 76.6%. GNSS observations were utilized to verify the improvement due to the removal of tropospheric noise. We found that LOS displacement with GACOS correction better fitted the GNSS observation than LOS displacement without GACOS correction. Therefore, atmospheric correction plays an important role in long-term InSAR-based observations, especially in avoiding any bias in the interpretation of the estimated time series

Mapping of pga value using psa method in West Halmahera North Maluku

The earthquake that occurred in the West Halmahera region was very detrimental, even though the human casualties were not very significant. But it will affect the stability and capacity of a region in terms of regional development. The mapping of earthquake-prone areas is carried out by a probabilistic seismic hazard analysis (PSHA) method to analyze soil movement parameters, namely Peak Ground Acceleration so that it can determine earthquake-prone areas in West Halmahera. The results of seismic hazard analysis show that the West Halmahera area is an area that is relatively prone to earthquake hazards because it is still strongly influenced by subduction (megathrust) earthquakes from the Philippine plate, Maluku sea and Sangihe. This is indicated by the value of earthquake acceleration on the Peak Ground Acceleration for the 500 year return period of around 0.38 - 3.69 g and 0.30 - 3.69 g for the 2500 year return period

The Effect of Differences Leachate Concentration and Material Properties on Electrical Conductivity of Volcanic Deposits – Case Studies Piyungan Landfill Bantul Yogyakarta

Monitoring at the contaminated subsurface soil, have been conducted by using the geophysical surface method, especially for geoelectrical resistivity method. Monitoring is commonly conducted by using geoelectrical resistivity through measuring the value of Electrical Resistivity (ER) or Electrical Conductivity (EC) of leachate contaminated soil layer. EC measurement value of soil is affected by many factors, among others, particle conduction of soil materials, surface conduction, fluid conduction in the pores as well as the effect of particle shape and soil materials. Piyungan landfill is the main disposal site of Yogyakarta municipal solid waste. This landfill located mainly on the tertiary rocks of volcanic rocks and its weathering products. In order to improve the accuracy of geoelectrical measurements on resistivity in monitoring soil layers from contaminated leachate on this area, this research conducted several measurements on physical properties of soil sample and electrical properties of leachate in the saturated soil samples. The measurement of physical properties includes: porosity, clay content, particle content, and cation exchange capacity (CEC) value. The soil samples were collected from 3 locations around Piyungan Landfill. Type of soils are taken from the alluvial deposits (Sample B), weathered tuffaceous sandstone-claystone (Sample D), and weathered andesitic breccia (Sample F). Samples were made in containers, saturated with aquades-leachate solution with 12 different concentration levels. Electrical conductivity (EC) was measured by using Soil Box Miller and Geoelectric Resistivity Oyo McOhm. According to results of physical properties analysis, the grain size of soils are dominantly sandy clayey silt in grain size distribution, with clay content ranging from 33.0--38.4 %, the CEC values ranging from 26.8--52.7 meq/100 gr, and the porosity of samples B, D and F is 58.85 %, 55.30 %, 59.24 %, respectively. Based on the experiments with 12 different leachate concentrations, there is a linear increase in EC of 0.718mS/cm for every increase in electrical conductivity pore fluid (ECf ) 1 mg/l in samples B, while in samples D and F are 0.492 mS/cm and 0.284 mS/cm respectively. Plotting the data of EC vs ECf for each samples and ER vs ECf , it can be concluded the slope ofDEC/DECf differ for each samples and the electrical conductivity value of different concentration of leachate is very sensitive for alluvial deposits compare to the weathered tuffaceous sandstone-claystone and weathered volcanic breccia deposits

SEISGAMA: A Free C# Based Seismic Data Processing Software Platform

Seismic reflection is one of the most popular methods in geophysical prospecting. Nevertheless, obtaining high resolution and accurate results requires a sophisticated processing stage. There are many open-source seismic reflection data processing software programs available; however, they often use a high-level programming language that decreases its overall performance, lacks intuitive user-interfaces, and is limited to a small set of tasks. These shortcomings reveal the need to develop new software using a programming language that is natively supported by Windows® operating systems, which uses a relatively medium-level programming language (such as C#) and can be enhanced by an intuitive user interface. SEISGAMA was designed to address this need and employs a modular concept, where each processing group is combined into one module to ensure continuous and easy development and documentation. SEISGAMA can perform basic seismic reflection processes. This ability is very useful, especially for educational purposes or during a quality control process (in the acquisition stage). Those processes can be easily carried out by users via specific menus on SEISGAMA’s main user interface. SEISGAMA has been tested, and its results have been verified using available theoretical frameworks and by comparison to similar commercial software

Analisis dan Model Inversi Gaya Berat 2D untuk Penampakan Sesar Palu Koro Di Sulawesi Tengah Indonesia

Analisis dan modeling mengenai struktur geologi Pulau Sulawesi khususnya wilayah Sulawesi Tengah sangat menarik sebab memiliki kompleksitas yang tinggi sebagai akibat interaksi dinamis dari tiga lempeng utama dunia. Ketiga lempeng tersebut yakni lempeng India Australia, lempeng Pasifik dan lempeng Eurasia yang dalam pergerakannya saling bertemu yang mengakibatkan daerah ini mengalami deformasi kerak bumi yang aktif. Salah satu bentuk deformasi dari gerakan dinamik adalah terbentuknya sesar Palu Koro. Metoda yang digunakan untuk mengkaji sesar tersebut digunakan metoda gayaberat. Hasil yang diperoleh menunjukkan bahwa sesar Palu Koro merupakan sesar geser mengiri dan normal. Model patahan bawah permukaan sesuai dengan penampakan morfologi topografi daerah penelitian. Bagian struktur bawah permukaan telah mengalami deformasi yang kuat dimana semua model strukturnya berbentuk struktur sekunder tidak ditemukan lagi struktur primer. Didapatkan pula batuan intrusi berkisar dari dua sampai tiga intrusi yang terlihat pada sayatan AA’. Formasi batuannya berjumlah enam jenis, yaitu batuan aluvium, formasi pakuli, formasi latimojong, kompleks wana, kompleks gumbasa dan batuan intrusi