Teraphan Ornthammarath

Bio: Teraphan Ornthammarath is an academic researcher from Mahidol University. The author has contributed to research in topics: Peak ground acceleration & Seismic hazard. The author has an hindex of 9, co-authored 24 publications receiving 265 citations. Previous affiliations of Teraphan Ornthammarath include University of Iceland & Asian Institute of Technology.

Probabilistic Seismic Hazard Macrozonation of Tamil Nadu in Southern India

Abstract: The south Indian state of Tamil Nadu in the peninsular shield is a zone of low to moderate seismic activity with a sparse historical record of significant earthquakes. The current intensity-based zoning adopted by the Indian seismic code stipulates an effective peak ground acceleration (PGA) of either 0.10 or 0.16 g for different parts of the state, for the maximum considered earthquake (MCE), and the service life of a structure. In the current study, probabilistic seismic hazard contour maps for Tamil Nadu and the union territory of Pondicherry, in terms of the ground-motion parameters, PGA and spectral accelerations, at 0.1, 0.5, and 1.0 sec for 2%, 5%, and 10% probabilities of exceedance in a 50 yr period, have been produced. Hazard computations have been performed over a grid of sites covering the territory at an interval of 0.2°. A comprehensive earthquake catalog has been compiled for the region extending between 2 and 20.7° N latitude and 68 and 88° E longitude and spanning ∼950 yrs. The hazard maps are produced by suitably accounting for epistemic uncertainty in the hazard computations within a logic-tree framework incorporating parameters such as different probabilistic hazard analysis methods (classical Cornell–McGuire and zone-free approaches), catalog completeness estimation methods, maximum cutoff magnitude, and ground-motion predictive equations for shallow crustal intraplate environments. The hazard maps are compared to the zoning prescribed by the seismic code. The current estimations show that the potential seismic hazard in considerable parts of the state is underestimated by the broad zoning adopted by the Indian Standards.

Probabilistic seismic hazard assessment for Thailand

Abstract: A set of probabilistic seismic hazard maps for Thailand has been derived using procedures developed for the latest US National Seismic Hazard Maps. In contrast to earlier hazard maps for this region, which are mostly computed using seismic source zone delin- eations, the presented maps are based on the combination of smoothed gridded seismicity, crustal-fault, and subduction source models. Thailand's composite earthquake catalogue is revisited and expanded, covering a study area limited by 0 ◦ -30 ◦ N Latitude and 88 ◦ -110 ◦ E Longitude and the instrumental period from 1912 to 2007. The long-term slip rates and esti- mates of earthquake size from paleoseismological studies are incorporated through a crustal fault source model. Furthermore, the subduction source model is used to model the mega- thrust Sunda subduction zones, with variable characteristics along the strike of the faults. Epistemic uncertainty is taken into consideration by the logic tree framework incorporat- ing basic quantities, such as different source modelling, maximum cut-off magnitudes and ground motion prediction equations. The ground motion hazard map is presented over a 10 km grid in terms of peak ground acceleration and spectral acceleration at 0.2, 1.0, and 2.0 undamped natural periods and a 5% critical damping ratio for 10 and 2% probabilities of exceedance in 50years. The presented maps give expected ground motions that are based on more extensive data sources than applied in the development of previous maps. The main findings are that northern and western Thailand are subjected to the highest hazard. The largest contributors to short- and long-period ground motion hazard in the Bangkok region are from the nearby active faults and Sunda subduction zones, respectively.

Assessment of ground motion variability and its effects on seismic hazard analysis: a case study for iceland

Abstract: Probabilistic seismic hazard analysis (PSHA) generally relies on the basic assumption that ground motion prediction equations (GMPEs) developed for other similar tectonic regions can be adopted in the considered area. This implies that observed ground motion and its variability at considered sites could be modelled by the selected GMPEs. Until now ground-motion variability has been taken into account in PSHA by integrating over the standard deviation reported in GMPEs, which significantly affects estimated ground motions, especially at very low probabilities of exceedance. To provide insight on this issue, ground-motion variability in the South Iceland Seismic Zone (SISZ), where many ground-motion records are available, is assessed. Three statistical methods are applied to separate the aleatory variability into source (inter-event), site (inter-site) and residual (intra-event and intra-site) components. Furthermore, the current PSHA procedure that makes the ergodic assumption of equality between spatially and temporal variability is examined. In contrast to the ergodic assumption, several recent studies show that the observed ground-motion variability at an individual location is lower than that implied by the standard deviation of a GMPE. This could imply a mishandling of aleatory uncertainty in PSHA by ignoring spatial variability and by mixing aleatory and epistemic uncertainties in the computation of sigma. Station correction coefficients are introduced in order to capture site effects at different stations. The introduction of the non-ergodic assumption in PSHA leads to larger epistemic uncertainty, although this is not the same as traditional epistemic uncertainty modelled using different GMPEs. The epistemic uncertainty due to the site correction coefficients (i.e. mean residuals) could be better constrained for future events if more information regarding the characteristics of these seismic sources and path dependence could be obtained.

A note on the strong ground motion recorded during the Mw 6.8 earthquake in Myanmar on 24 March 2011

Abstract: This study aims to investigate a Mw 6.8 earthquake that occurred in Myanmar on 24 March 2011. The epicenter of this earthquake struck very close to the Tarlay town which is located near the border of Myanmar, Lao People’s Democratic Republic (PDR), and Thailand. In addition, this shallow left-lateral strike-slip earthquake occurred on Nam Ma fault which is previously identified as an active fault. Based on instrumental earthquake catalogue, Nam Ma fault did not produce any earthquake greater than magnitude 6 for at least 100 years. So the 24 March 2011 earthquake is essentially filling the gap of relatively short instrumental earthquake catalogue in this region. The strong ground motion from this event has been recorded in Thailand with the highest peak ground acceleration (PGA) of 0.20 g at 28 km distance at Mae Sai town. Comparison between observed strong motion and global empirical equation had been provided. Over the distance range for which the model is applicable, they are in fair agreement. On the other hand, at long distance, the large positive and negative residuals suggest that a change in slope in the attenuation is not reflected in these relations. Lastly a seismological aspect of strong ground motion at Mae Sai had been given.

5 May 2014 MW 6.1 Mae Lao (Northern Thailand) Earthquake: Interpretations of Recorded Ground Motion and Structural Damage:

Abstract: A moderate left-lateral strike-slip earthquake of MW 6.1 occurred on 5 May 2014 in northern Thailand, causing damage to the town of Mae Lao and nearby municipalities. Based on an instrumental earth...

Ground Motion Characteristics Estimated from Spectral Ratio between Horizontal and Verticcl Components of Mietremors.

Abstract: The spectral ratio between horizontal and vertical components (H/V ratio) of microtremors measured at the ground surface has been used to estimate fundamental periods and amplification factors of a site, although this technique lacks theoretical background. The aim of this article is to formulate the H/V technique in terms of the characteristics of Rayleigh and Love waves, and to contribute to improve the technique. The improvement includes use of not only peaks but also troughs in the H/V ratio for reliable estimation of the period and use of a newly proposed smoothing function for better estimation of the amplification factor. The formulation leads to a simple formula for the amplification factor expressed with the H/V ratio. With microtremor data measured at 546 junior high schools in 23 wards of Tokyo, the improved technique is applied to mapping site periods and amplification factors in the area.

The New Zealand Active Faults Database

Abstract: The New Zealand Active Faults Database (NZAFD) is a national geospatial database of active faults – including their locations, names and degrees of activity – that have deformed the ground surface of New Zealand within the last 125,000 years. The NZAFD is used for geological research, hazard modelling and infrastructure planning and is an underlying dataset for other nationally significant hazard applications such as the National Seismic Hazard Model. Recent refinements to the data structure have improved the accuracy of active fault locations and characteristics. A subset of active fault information from the NZAFD, generalised for portrayal and use at a scale of 1:250,000 (and referred to as NZAFD250), is freely available online and can be downloaded in several different formats to suit the needs of a range of users including scientists, governmental authorities and the general public. To achieve a uniform spatial scale of 1:250,000 a simplification of detailed fault locational data was required ...

Probabilistic Seismic Hazard Assessment of India

Abstract: Online material : Data files for seismogenic source zones (polygons), smoothed-gridded seismicity models, and hazard curves at 0.2° regular grid spacing over the study region. Earthquake disasters occur mainly due to the collapse of buildings and structures triggered by ground motions. It is, therefore, important to predict ground-shaking levels in order to determine appropriate building code provisions for earthquake-resistant design of structures. This involves extensive analyses and development of appropriate seismological models; namely, seismogenic sources, seismic site conditions, and ground motion predictions. The hazard products, viz . data and maps, constitute important tools for framing public policies toward land-use planning, building regulations, insurance, and emergency preparedness. View this table: Table 1 Major Earthquake Casualties during 1900–2008 in India and Adjoining Regions In India, several events during the last 100 years, as listed in Table 1, indicate that even moderate earthquakes ( MW < 7.0) can cause significant devastation. On one hand, ongoing urbanization and unprecedented population growth have considerably aggravated the prevailing seismic risk. On the other hand, the available seismic hazard maps covering the entire country are about a decade old. Consequently an updated seismic hazard model for the country is imperative and necessitated by new data, recent findings, and methodological improvements. In the present study, we make a case for new probabilistic seismic hazard analysis (PSHA) of India. The fundamental studies have been carried out to deliver the hazard components, including seismogenic source zonation and seismicity modeling in the Indian subcontinent (Thingbaijam and Nath 2011), assessment of site conditions across the country (Nath, Thingbaijam, Adhikari et al. 2011), and a suitability test for the ground-motion prediction equations in the regional context (Nath and Thingbaijam 2011). These components are integrated to deliver a preliminary model consisting of spatial distributions of peak ground acceleration (PGA) and 5%-damped pseudo spectral acceleration (PSA). Initial attempts at …

Estimating ground motions using recorded accelerograms

Abstract: A procedure for estimating ground motions using recorded accelerograms is described. The premise of the study is the assumption that future ground motions will be similar to those observed for similar site and tectonic situations in the past. Direct techniques for scaling existing accelerograms have been developed, based on relative estimates of local magnitude,M L . Design events are described deterministically in terms of fault dimension, tectonic setting (stress drop), fault distance, and site conditions. A combination of empirical and theoretical arguments is used to develop relationships betweenM L and other earthquake magnitude scales. In order to minimize scaling errors due to lack of understanding of the physics of strong ground motion, the procedure employs as few intermediate scaling laws as possible. The procedure conserves a meaningful measure of the uncertainty inherent when predicting ground motions from simple parameterizations of earthquake sources and site conditions.

The GEM Global Active Faults Database

Abstract: The GEM Global Active Faults Database (GAF-DB) is the first public, comprehensive database of active faults with worldwide coverage. The GAF-DB is a compilation of many regional datasets. The GAF-D...