Central Geological Survey Research Articles

Hear Wave Velocity Analysis Based on Two Rock Layers Modeling Using Microtremor Data of Gresik and Surrounding Areas

The lithology on the surface in the current condition is often found to be not a fresh rocks, but all materials, be it alluvial, soil, backfill soil, or rocks with a very high degree of weathering. Therefore, this study was conducted to estimate the type of layer on the surface and its underlying layer based on the analysis of Vs (shear wave velocity) values in the surface lithological media and the underlying layer through the modeling of two rock layers. To complete this research, microtremor array data was collected by the Geological Survey Center in the Gresik area which was then processed using the SPAC (Spatial Autocorrelation) method. Based on the results of the study, the Gresik area has a surface Vs value that still shows soft soil values in the range of 65 - 170 m/s and its basement Vs already shows fresh rocks to older lithologies in the alluvial area in the range of 150 - 435 m/s, so it can be seen that some areas that should consist of a fairly hard lithology in the Gresik area have changed with a fairly high level of weathering.

Identification of shale gas existence based on 2-dimensional magnetotelluric data in the Kutai basin, East Kalimantan, Indonesia

Research on unconventional methods in the shale gas exploration process has begun to be developed to meet the demand for oil and natural gas sustainability. The research area is located in the Kutai Basin, East Kalimantan, Indonesia. The current study from the Geological Survey Center shows that the Kutai Basin has 46.79 TCF of shale gas potential. The magnetotelluric (MT) method was applied in this study to describe the distribution of subsurface resistivity values. The inversion schemes performed in the MT method are 1-dimensional and 2-dimensional inversions. In this study, there are 8 measurement stations in one line. The presence of low resistivity values or conductive zones identifies the potential for black shale layers. The potential for shale gas is suspected to be detected at station KT29, which is included in the Pamaluan Formation, and at stations KT12, KT31, KT13, and KT15, which are included in the Pulaubalang Formation, because it is associated with source rock from petroleum in the Kutai Basin system, as supported by previous research data.

Occurrence and influencing factors of high groundwater manganese in the oxbow lakes of the middle reaches of Yangtze River

Occurrence and influencing factors of high groundwater manganese in the oxbow lakes of the middle reaches of Yangtze River

Bawean Geotrack: Linkage Between Geodiversity, Biodiversity, And Cultural Diversity for Driving The Acceleration Bawean Island-Gresik Geopark

Bawean Island, Gresik Regency is geographically located in the Java Sea, precisely located between Borneo and Java. Currently, Bawean Island is being fought to become a Geological Heritage and continues to be developed, so that it can be proposed as a National Geopark. The Geology, Biology, and Cultural Diversity that exists on Bawean Island are still separate pieces that need further research so that it can be presented in a holistic order as geotourism. The purpose of this study is to examine geosite recommendations on Bawean Island and to reconstruct the geological history of the biological and cultural diversity of the community that developed from the past to the present in a Geosite Distribution Path Map (Geotrack). The methods used are literature review, observation of DEM imagery to determine morphology, and Geosite Potential Survey which is followed by feasibility study calculations based on parameters from the Geological Survey Center. The results of this study are in the form of a Geotrack Map consisting of 24 Geosites (15 Geodiversity, 3 Biodiversity, and 6 Cultural Diversity) which are contained in a digital system in the form of WebGIS so that all elements of society can access it. The occurrence of transgression and marine regression in the past caused by the formation of ancient volcanoes supports the formation of a typical flora and fauna ecosystem on Bawean Island. In addition, the formation of an island in the middle of the Java Sea surrounded by other cultures and civilizations led to the acculturation and cultural assimilation of the Bawean island.

North Pacific Water Mass Contribution in the Northern Sea of Lembata Island, East Nusa Tenggara

As the Indonesian Throughflow (ITF) passes through the Flores Sea, we expect it will affect the water mass character in the northern sea of Lembata Island. Therefore, we examined the contribution of North Pacific (NP) water mass, i.e., the North Pacific Subtropical Water (NPSW) and the North Pacific Intermediate Water (NPIW) in the study area. We used 30 CTD casts from OTEC Geological Survey Center Expedition 2017 and ARGO float data, analyzed through the TS diagram and Optimum Multiparameter (OMP). The remnant of the NPSW (NPIW) core layer was found at 140-190 (220-330) m depth, deeper than it occurs in the NP source regime, and of previous pathway seas i.e. Makassar Strait. The OMP results show NPSW (NPIW) contribution is about 20-75 (50-70)%. Contrary to the ITF direction from the western pathway, the value of NP water mass contribution is larger in the eastern than in the western part of the northern sea of Lembata Island. We speculated the ITF flows away from the northern sea of Lembata Island, blocked by the headland in the eastern part of Flores Island. Then a small part of ITF is deflected back to the west, but unfortunately, no detailed current is available in the study area.

Study of Boalemo Red Limestone for Geotourism Development based on Lithological, Geochemical Analysis and Geological Heritage Assessment

Indonesia has very diverse and unique rocks that have the potential to become a geological heritage. Based on the existing potential, an integrated management system is needed so that it can be utilized for the welfare of the community, one of which is a geopark. Gorontalo has a rock distribution consisting of several formations, one of which is the Tinombo Formation which is the oldest formation. In this formation there is red limestone which has great potential due to its rarity so that it can be developed into a site in the development of a geopark in Gorontalo. The purpose of this research is to conduct a geosite assessment of geological features in Boalemo Regency as a basis for developing geotourism in Boalemo Regency, Gorontalo. The research site is located in Dimito Village, Wonosari Subdistrict and Lahumbo Village, Tilamuta Subdistrict, Boalemo Regency, Gorontalo Province. The methods used in this research are lithological analysis, Geochemical analysis and geosite potential analysis using the technical guidelines for geological heritage resource assessment by the Geological Survey Center. The results showed that the red color-controlling minerals in limestone are hematite and rodoxite, the red color-controlling chemical elements in limestone are SiO2, MnO, Fe2O3, Sr and CaO. The results of the assessment of geological features explain that the Wonosari Red Limestone Site and the Tilamuta Red Limestone Site are included in the medium category. Geosite Red Limestone can be developed as an object of study in the field of education by utilizing natural laboratories for the development of geoparks in Gorontalo.

ANALYSIS AND QUANTITATIVE ASSESSMENT OF GEODIVERSITY AT KARYA MURNI, GORONTALO, INDONESIA

Karya Murni is one of the areas in the northern arm of Sulawesi that has been tectonically influenced. Tectonic processes have implications for the formation of rocks and geological features that have the potential to be developed into geodiversity sites. The development of geological features as a geodiversity site in aspiring geopark Gorontalo can protect valuable geological features from frequent degradation. This research aims to analyze and conduct quantitative assessments of geological diversity in Karya Murni, Gorontalo. The research method used is field observation, laboratory analysis, and geodiversity assessment. Field observations included observing landform, collecting rock samples, and measuring geological structures. Field observations were also carried out to observe aspects of the geodiversity assessment which included science, education, tourism, and risk degradation. Laboratory analysis consists of geomorphological analysis, petrographic analysis, and geological structure data analysis. Geodiversity assessment uses the Geological Survey Center of Indonesia assessment. The results suggest that the geomorphology of the study area can be divided into four geomorphic units - the volcanic hills, denudational hills, Karst hills, and fluvial plain units. The stratigraphy of the research area is divided into four units from the age of the early Eocene to the Holocene - the andesite lava, volcanic breccia, reef limestone, and alluvial deposit units. The geological structure of the study area is a trending northeast–southwest to northwest–southeast. Active faults at the location of the study area consist of the Apitalawu normal fault. At recent states, generally geosites of the Karya Murni have moderate scientific values, the low educational and touristic values and high risk of degradation. The geodiversity potential of the research area can be utilized for further research and education.

A Study on the Reasons for No Soil Liquefaction Occurring in the Lanyang Plain in a Strong Earthquake Area

The Lanyang Plain is prone to earthquakes of magnitude 5 or higher. The Central Geological Survey’s soil liquefaction potential map of Yilan County shows that more than 69% of the plain area has high liquefaction potential: but why have there not been any liquefaction cases in the past 23 years? Based on the results of the groundwater pumping test, geological history, and the soil liquefaction analysis method, this study aimed to explore and analyze the causes of no liquefaction occurring in the Yilan region. To understand the permeability of the overall stratum structure of the Lanyang Plain and the spring phenomenon, the relationship between groundwater well-pumping test results and the permeability coefficient experience formulas was first studied. Then the Chapuis’ experience formula of the K value multiplied by 10 was recommended herein such that the permeability coefficient K values of the Lanyang plain could be estimated with large numbers. The reasons for the absence of liquefaction cases in Lanyang plain were then investigated. It was found that less serious earthquakes occurred and combined with the extremely ideal permeable soil conditions existing in the Lanyang plain, this led to no catastrophic liquefaction cases occurring over the last 23 years.

The Investigation of Shallow Structures at the Meishan Fault Zone with Ambient Noise Tomography Using a Dense Array Data

Seismic monitoring relies on seismography. However, the high cost of seismic equipment has presented a challenge to increasing the density of seismic networks in previous decades. Due to the large station spacing and inferior coverage of stations, this situation has led to a loss of detail in many research results. Along with the improvement of technology, the problem of increasing the density of seismographic observations is no longer an impossible issue. This makes it feasible to deploy a dense seismic network for monitoring earthquakes. This study deployed a linear dense array across the Meishan Fault in west-southern Taiwan for the purpose of analyzing the shallow fault zone structure. While the 1906 Meishan earthquake occurred in a period when historic records were available, the surficial geology surveys of the Meishan Fault are challenging because farming and construction engineering have obscured the outcrop. Early surveys of the Meishan Fault were mainly seismic surveys. In recent decades, over thirty profiles have been completed. However, the reflection seismic records had poor signal-to-noise ratios because the Meishan Fault is buried under thick sediments. Thus, the shallow structure of the Meishan Fault is still not known in detail. This study applied double-beamforming tomography to a dense seismic array to obtain high-resolution images of the Meishan Fault zone. The result shows that there is a south-dipping interface near the fault trace as indicated by the Central Geological Survey of Taiwan. In addition, we observed velocity transitions of perturbation profiles that may be caused by a branch fault, the Chentsoliao Fault. This study demonstrates that the ambient noise double beamforming method is an effective tool for imaging the detailed shallow structure along with the dense seismic array.

PERENCANAAN DESAIN INTERIOR PUSAT INFORMASI GEOLOGI BELITUNG TIMUR DENGAN PENERAPAN IDENTITAS BUDAYA LOKAL

This research is an Interior Design Planning process for the Geological Information Center (GIC) Building in East Belitung, which applies the characteristics of East Belitung's cultural identity. This research was motivated by a plan from the Geological Survey Center, Geological Agency of the Ministry of Energy and Mineral Resources in 2019, which was the need for the availability of GIC Buildings and Interiors specifically for the East Belitung district. The facility will later function as an Information Center regarding the diversity of rock types contained in the earth of Belitung, which will become one of the geotourism destinations. The purpose of this research is to produce an Interior design of the East Belitung GIC that applies the cultural characteristics of Belitung, with a form that combines modern style in Modern Facilities with elements of local culture as a distinctive feature. The design process is carried out through an interior design planning approach.

Management of Site Evaluation: A Lesson Learnt of 10 MW HTGR Experimental Power Reactor (RDE) Project Site Licensing

In 2013, a pre-project activity of Experimental Power Reactor (RDE Project) was started. The reactor type is a High Temperature Gas-cooled Reactor (HTGR) with a 10 MWth capacity. At present the project has been postponed due to some reason, however, there was an important stage that has been achieved, regarding the site evaluation process to obtain site permits from the Regulatory Body (BAPETEN). Site evaluation is an critical activity that will guarantee the safety of nuclear facilities from natural and human induced external events as well as the safety of population and the environment due to nuclear facility accidents. Site evaluation for the RDE project has the same process as a large NPP project, considering that at the time of the site evaluation process there were no specific regulations that considered a graded approach for a mini-scale NPP. The site evaluation process includes two stages, namely 1). Site Evaluation Program (SEP) and Management System of Site Evaluation (MSSE) Approval and 2) Site Evaluation Approval. SEP is intended to establish the scope and criteria for site evaluation safety. Whereas the Site Evaluation Management System is a managerial instrument that makes site safety as the top priority in each activity and process of RDE site evaluation. BATAN as the project owner delivered the SEP document and MSSE to BAPETEN on March 10, 2014. These documents was intensively discussed by BAPETEN and BATAN to determine agreement on the scope of site evaluation, criteria and management aspects based on site safety considerations. The technical aspects that must be evaluated are seismicity, volcanic hazard, geotechnical and foundation, meteorology, hydrology, human induced events, dispersion and population distribution. This document was approved by BAPETEN on March 2, 2015. Considering the very wide scope with various fields of competence and need supporting data for evaluation, this can not be done only by BATAN experts, it must collaborate with various institution that have competence related to the site aspect. The experts that involved in the site evaluation come from Meteorology and Geophysics Agency (BMKG) for seismic and meteorological aspects, Geospatial Information Agency (BIG) to support geospatial data and ground movements/deformation, Geological Survey Center (PSG) to support geological data and geological structures, Center for Volcanology and Geological Disaster Mitigation (PVMBG) to support volcanic catalog data and volcanic hazard, University to support geotechnical, foundation and hydrology evaluation. BATAN experts from various Centers involved for evaluating topography, human induced events, dispersion, dose assessment, population distribution, emergency preparedness, and technology aspects. Data acquisition activities such as geophysics, drilling, geological mapping, volcanic mapping, hydrology, satellite imagery and digitizing processes are contracted through third parties with guidance developed by the BATAN Expert Team. Considering the very limited time and financial resources availability, in order to achieve the effectiveness of all activities, a special organization was formed to control site evaluation with the BATAN Chairman as Top Management. The Site evaluation document was submitted in two stages. The first stage is administrative completeness and it was declared administratively complete on November 15, 2015. The second step is BAPETEN assessed and evaluated the technical documents submitted to determine the acceptability of the site. The process of evaluating the site evaluation document lasts quite a long and intensive. Finally, the site permit was issued on January 23, 2017. The valuable lessons during the site evaluation project are: 1) It require the same understanding and perception between applicant and regulator regarding the site licensing process; 2) The establishment and implementation of an effective organization; 3) controlling the project schedule.

ASESMEN NILAI-NILAI PARIWISATA TERHADAP FITUR GEOLOGI DAERAH BONGO DAN SEKITARNYA SEBAGAI DASAR PENGEMBANGAN GEOWISATA DI PESISIR SELATAN GORONTALO

Geology is an important aspect in the development of tourism in an area. One of the attractions in a natural tourism location is certainly highly controlled by the geological setting in the area. The purpose of this research is to assess tourism values of geological features in the Bongo and surrounding areas as a basis for developing geotourism on the southern coast of Gorontalo. The research location is at coordinates N 00029’42” - N 00029’51” and E 12301’26” - E 12303’32”. The method used in this study is a surface geological survey, which includes field data collection in the form of lithology, geological structure and geomorphology. The standard used for assessing tourism values is the technical guide for assessing geological heritage resources by the Geological Survey Center. The results showed that the lithology unit of the study area consists of granite, volcanic breccia and reef limestone. The geological structure in the research area is shear fracture with main stress that relatively directed to northwest-southeast. The geomorphic unit of the study area consisted of two units, namely volcanic hills, and marine units. The results of the assessment of tourism values on geological features explain that the Bongo and surrounding areas are included in the medium category. Improvements are needed on low value criteria, namely vulnerability, relationships with other values, and economic level.

SOUTH NATUNA BASIN RECONFIGURATION BASED ON RECENT SEISMIC AND GRAVITY SURVEYS

The Geological Survey Center has conducted a seismic survey in the southern Natuna Sea region to obtain geological information below relating to the potential energy resources of the area. The area research is located in the western part and outside the Singkawang Basin area (BG, 2008), which is separated by a Metamorf ridge. 2D seismic survey results show 3 different rock units, namely shallow marine sedimentary rocks, tertiary sedimentary rocks and pre-Tertiary sedimentary rocks, with pre-Tertiary sediment depths of less than 2000 ms. Interpretation of seismic data shows the pattern of graben structures that form sub-basins. strong refl ectors seen in seismic record can distinguish pre-rift, syn-rift and post-rift deposits. There are 2 wells, namely Datuk 1X and Ambu 1X. Datuk 1X has a depth of 1187 meters, and The Ambu 1X has a depth of 880 meters that is crossed by a seismic line. Both drilling has obtained Tertiary aged sandstone that covers pre-Tertiary bedrock.Gravity anomaly data in the seismic region shows anomaly values between 10 to 54 mgal which form the anomaly ridge and basinThe ridge anomaly extends as an anticline, while the anomaly basin also rises to form a syncline. Sincline and anticline trending southwest - southeast, with widening and narrowing patterns.Based on its geological model, the depth of the sediment is relatively shallow between 1500 to 2000 meters. While the integration between seismic, gravity and geomagnetic data shows the discovery of new basins that have never been described before.Finally, the integration of seismic and gravity data succeed discovers a new basin which has never been delineated before. In addition, it shows the continuity of the regional geological structure spanning from the studied area to the West Natuna Basin which is well known to be rich in hydrocarbon potential.

Estimation of Seismic Ground Motions and Attendant Potential Human Fatalities from Scenario Earthquakes on the Sanchiao Fault in Taipei City, Taiwan

The purpose of this study is to estimate maximum ground motions in Taipei city in the form of ShakeMaps as well as to assess potential human fatalities from scenario earthquakes on the Sanchiao active faults in this area. Analysis of seismic hazard potential becomes necessary in Taipei City for the Central Geological Survey (CGS) announced the Sanchiao active fault as Category II. The resultant ShakeMap patterns of maximum ground motion by using ground motion prediction equation (GMPE) method in a case of Mw6.88 show the areas of PGA above 400 gals are located in the northern and western parts of Taipei. Furthermore, the areas of PGA above 500 gals are located in these regions: Beitou, Shihlin, Datong, Wanhua, Jhongjheng, northern Neihu, western Jhongshan, western Daan and western Sinyi. In addition, seismic hazards in terms of PGA and PGV in the vicinity of the Sanchiao fault are not completely dominated by the Sanchiao fault. The main reason is that some areas located in the vicinity of the Sanchiao fault are marked with low site response amplification values of 0.55 and 0.67 for PGA and PGV, respectively. Finally, from estimation of potential human fatalities from scenario earthquakes on the Sanchiao active fault, it is noted that potential fatalities increase rapidly in people above age 45. Total fatalities reach a high peak in age groups of 55–64. Another to pay special attention is Taipei City has hundreds of thousands of households whose residences over 40 years old. When a strong earthquake strikes, these old houses are vulnerable to collapse. In light of the results of this study, the author urge both the municipal and central governments to take effective seismic hazard mitigation measures in the highly urbanized areas with a large number of old buildings in Taipei city. The results of this study will show which areas with higher earthquake hazard potential in Taipei City. It will help mitigate Taipei City earthquake disaster loss in the future, as well as provide critical information for emergency response plans.

Framework for susceptibility analysis of layered rock slopes considering the dimensions of the mapping units and geological data resolution at various map scales

Abstract In Taiwan, the failure of rock slopes has caused the catastrophic loss of lives and property. To understand the risks associated with rock slope failure, susceptibility analysis has been widely adopted as a fundamental task. However, currently, most susceptibility analyses have investigated only landslide occurrences and have been limited to the regional scale. In this case, susceptibility maps cannot provide detailed information about the rock slope stability as required by the engineers. To fill this gap, this study developed a methodological framework to analyze the susceptibility of layered rock slopes from regional to local scales. In each map scale, the appropriate size of the slope unit (SU) was produced as the mapping unit through the object-based image analysis (OBIA) method, and the susceptibility map was generated with an explicit purpose according to the resolution of geological data. Multiscale susceptibility analysis of layered rock slopes was performed in a metamorphic area in northern Taiwan. The performance of the susceptibility maps was validated by the field investigations and the data of the geologically sensitive area, which were released by the Central Geological Survey of Taiwan. The results show that different phases of the evaluation of rock slope stability were addressed, including the landslide activity and the rock slope characterization on the regional scale and the failure mechanisms on the local scale. In addition, suitable SUs can also be semiautomatically reproduced by the OBIA method with suggested strategies.

Failure Impact Assessment for Large-Scale Landslides Located Near Human Settlement: Case Study in Southern Taiwan

In 2009, Typhoon Morakot caused over 680 deaths and more than 20,000 landslides in Taiwan. From 2010 to 2015, the Central Geological Survey of the Ministry of Economic Affairs identified 1047 potential large-scale landslides in Taiwan, of which 103 may have affected human settlements. This paper presents an analytical procedure that can be applied to assess the possible impact of a landslide collapse on nearby settlements. In this paper, existing technologies, including interpretation of remote sensing images, hydrogeological investigation, and numerical analysis, are integrated to evaluate potential failure scenarios and the landslide scale of a specific case: the Xinzhuang landslide. GeoStudio and RAMMS analysis modes and hazard classification produced the following results: (1) evaluation of the failure mechanisms and the influence zones of large-scale landslides; (2) assessment of the migration and accumulation of the landslide mass after failure; and (3) a landslide hazard and evacuation map. The results of the case study show that this analytical procedure can quantitatively estimate potential threats to human settlements. Furthermore, it can be applied to other villages and used as a reference in disaster prevention and evacuation planning.

SPATIAL RESOLUTION EFFECTS OF DIGITAL TERRAIN MODELS ON LANDSLIDE SUSCEPTIBILITY ANALYSIS

The purposes of this study are to identify the maximum number of correlated factors for landslide susceptibility mapping and to evaluate landslide susceptibility at Sihjhong river catchment in the southern Taiwan, integrating two techniques, namely certainty factor (CF) and artificial neural network (ANN). The landslide inventory data of the Central Geological Survey (CGS, MOEA) in 2004-2014 and two digital elevation model (DEM) datasets including a 5-meter LiDAR DEM and a 30-meter Aster DEM were prepared. We collected thirteen possible landslide-conditioning factors. Considering the multi-collinearity and factor redundancy, we applied the CF approach to optimize these thirteen conditioning factors. We hypothesize that if the CF values of the thematic factor layers are positive, it implies that these conditioning factors have a positive relationship with the landslide occurrence. Therefore, based on this assumption and positive CF values, seven conditioning factors including slope angle, slope aspect, elevation, terrain roughness index (TRI), terrain position index (TPI), total curvature, and lithology have been selected for further analysis. The results showed that the optimized-factors model provides a better accuracy for predicting landslide susceptibility in the study area. In conclusion, the optimized-factors model is suggested for selecting relative factors of landslide occurrence.

SPATIAL RESOLUTION EFFECTS OF DIGITAL TERRAIN MODELS ON LANDSLIDE SUSCEPTIBILITY ANALYSIS

Abstract. The purposes of this study are to identify the maximum number of correlated factors for landslide susceptibility mapping and to evaluate landslide susceptibility at Sihjhong river catchment in the southern Taiwan, integrating two techniques, namely certainty factor (CF) and artificial neural network (ANN). The landslide inventory data of the Central Geological Survey (CGS, MOEA) in 2004-2014 and two digital elevation model (DEM) datasets including a 5-meter LiDAR DEM and a 30-meter Aster DEM were prepared. We collected thirteen possible landslide-conditioning factors. Considering the multi-collinearity and factor redundancy, we applied the CF approach to optimize these thirteen conditioning factors. We hypothesize that if the CF values of the thematic factor layers are positive, it implies that these conditioning factors have a positive relationship with the landslide occurrence. Therefore, based on this assumption and positive CF values, seven conditioning factors including slope angle, slope aspect, elevation, terrain roughness index (TRI), terrain position index (TPI), total curvature, and lithology have been selected for further analysis. The results showed that the optimized-factors model provides a better accuracy for predicting landslide susceptibility in the study area. In conclusion, the optimized-factors model is suggested for selecting relative factors of landslide occurrence.

First appearance datum of the Silurian graptolite Oktavites spiralis, and its evolution on the northern margin of South China

Wang, X., Wang, J. & Zhang, J., May 2016. First appearance datum of the Silurian graptolite Oktavites spiralis, and its evolution on the northern margin of South China. Alcheringa 41, xxx–xxx. ISSN 0311-5518.Xin Wang [wx200315046@163.com], Early Life Institute and State Key Laboratory of Continental Dynamics, Department of Geology, Northwest University, Xian 710069, PR China & Research Center for Orogenic Geology, Xian Geological Survey Center, China Geological Survey, Xian 710054, PR China; Jian Wang [332891824@qq.com], Ju Zhang [710726657@qq.com], Research Center for Orogenic Geology, Xian Geological Survey Center, China Geological Survey, Xian 710054, PR China.Graptolites represent the standard tools for biozonation and correlation of Ordovician and Silurian strata. Oktavites spiralis, one of the index graptolite species of the Telychian Age (late Llandovery, Silurian), is of great significance in biostratigraphy. However, the broad definition of the species and the lack of data on its evolutionary changes have led to controversies regarding its stratigraphic range and, consequently, to difficulties in regional correlations. Recent investigations in multiple Telychian profiles in the Ziyang–Langao area, along the northern margin of South China, reveal that the first appearance datum of Oktavites spiralis is located at the base of the Spirograptus turriculatus Zone, and its last appearance datum lies at the top of the Cyrtograptus lapworthi Zone (Telychian stage). The thecae vary markedly up-section and such change is consistent across all studied sections. This morphological change can be used as the basis for accurate stratigraphic subdivision and, hence, for effective regional correlation. In addition, this species has a wide range in population size and population density relative to other coexisting graptolite species, and can be better distinguished by using a more precise set of criteria.

Earthquake Probability Assessment for the Active Faults in Central Taiwan: A Case Study

Frequent high seismic activities occur in Taiwan due to fast plate motions. According to the historical records the most destructive earthquakes in Taiwan were caused mainly by inland active faults. The Central Geological Survey (CGS) of Taiwan has published active fault maps in Taiwan since 1998. There are 33 active faults noted in the 2012 active fault map. After the Chi-Chi earthquake, CGS launched a series of projects to investigate the details to better understand each active fault in Taiwan. This article collected this data to develop active fault parameters and referred to certain experiences from Japan and the United States to establish a methodology for earthquake probability assessment via active faults. We consider the active faults in Central Taiwan as a good example to present the earthquake probability assessment process and results. The appropriate ＂probability model＂ was used to estimate the conditional probability where M ≥ 6.5 and M ≥ 7.0 earthquakes. Our result shows that the highest earthquake probability for M ≥ 6.5 earthquake occurring in 30, 50, and 100 years in Central Taiwan is the Tachia-Changhua fault system. Conversely, the lowest earthquake probability is the Chelungpu fault. The goal of our research is to calculate the earthquake probability of the 33 active faults in Taiwan. The active fault parameters are important information that can be applied in the following seismic hazard analysis and seismic simulation.