Dirk Hollnack - Academia.edu (original) (raw)
Papers by Dirk Hollnack
Geophysical Journal International, 2001
Local seismic activity has been monitored in the southern part of the Kenya Rift in the area arou... more Local seismic activity has been monitored in the southern part of the Kenya Rift in the area around Lake Magadi. An earthquake recording network consisting of 15 station sites was operated for 8 months from November 1997 to June 1998. During this period, the Magadi area proved to be seismically active. Approximately 10 events per day were detected and found to be equally distributed over the rift floor. The hypocentre depth distribution shows surprisingly large depths of up to 27 km in the south and much shallower depths in the northern part of the area. Apart from the background activity, swarm activity with rates of more than 300 events per day was also recorded. The epicentres are clustered and trace a linear structure lying SSW-NNE over a length of 10 km north of Lake Magadi. Hypocentres in the region of the earthquake cluster are shallow and exhibit a sharp cutoff at 9 km depth. A surface crack that occurred during the recording period is connected to the earthquake swarm. Analysis of the focal mechanisms of selected earthquakes indicates predominantly normal faulting in response to a WNW-ESE-directed tensional stress field. This direction corresponds to the general alignment of the southernmost part of the Kenya Rift and to the surface faulting pattern inside the rift. The crustal structure of the area has been investigated using local earthquake tomography and the spatial distribution of hypocentres. The main results of the tomography are a linear positive velocity anomaly following the rift axis and a negative anomaly at shallow depth underneath Lake Magadi. The high velocities can be explained by mafic material that has intruded into the upper crust. The negative anomaly is attributed to highly fractured rocks. Maximum hypocentre depths indicate a body of low shear strength centred at the rift axis and a general deepening of the brittle-ductile transition from north to south.
Geothermics, 1989
Monitoring the natural selsmlcity of Milos island over a four month period led to the conclusion ... more Monitoring the natural selsmlcity of Milos island over a four month period led to the conclusion that the microselamlc activity is concentrated mainly in the central-eastern part of the island In the depth range from 5-8 km. Tomogrsphic inversion of 90 selected events led to a refined veloclty-depth distribution. The fluctuation of velocities appears to be depth-dependent; a remarkable horizontal change of velocities was found for the upper few kllometres of the crust, while at greater depths the crustal velocity is more homogeneous. Minima of the v,Jv=-ratlo coincide with the locations of the production wells in the Zefyrla Plain and close to Adamas, thus indicating higher temperatures in these areas. Faultplane solutions indicate that tensional stress in a NE-SW direction is the actual cause of the seismic activity. The frequency-magnltude relation indicates tectonic activities rather than volcanic.
Disaster Risk …, 2004
The growing loss burden from natural disasters requires a cooperative effort from all parties inv... more The growing loss burden from natural disasters requires a cooperative effort from all parties involved in order to finance, mitigate and reduce the losses from future catastrophic events. The affected stakeholder groups encompass the private sector, i.e. property owners, the financial sector and public authorities, i.e. government bodies on all administrative levels, but also non-governmental institutions and supra-or international organizations. Most important within the financial sector are the insurance and specifically the reinsurance industries, but also banks and the capital market as a whole can play a supportive role in risk financing. Under the heading of "risk partnership" the responsibilities of the persons and entities affected, of the financial sector and the state are described from an international perspective based on actual business practice. It is a challenging task to develop solutions which combine efficient incentives for property owners to undertake risk reduction measures with acceptable and affordable insurance conditions. A close and well-conceived cooperation especially between the state and the insurance sector is indispensable to achieve this goal. Various solutions have been designed and even implemented, but so far none of these have succeeded to a satisfactory degree. The potential role of the insurance sector in risk mitigation is addressed, and some examples of private/public partnerships working in the direction of risk reduction are presented.
Journal of African Earth Sciences, 1998
In 1990 the Geology Department of the University of Nairobi started to build up a seismological n... more In 1990 the Geology Department of the University of Nairobi started to build up a seismological network for Kenya, which has been operating since 1993. In this paper the actual state of this seismological network is described. Additionally, the first results on the seismic activity in the southern part of Kenya and adjacent areas between October 1993 and August 1996 are presented and are compared with historical data. Out of more than 2000 recorded local earthquakes 435 could be localised within the study area with local magnitudes of up to 5. The distribution of the events shows three areas of prominent seismicity: the Rift Valley between Nakuru and northern Tanzania; the area northeast of Kilimanjaro; and the Nyanza Rift in western Kenya. In a first attempt to assess the seismic hazard for the study area, a seismic energy map for the period of observation is given. o 1998 Elsevier Science Limited.
Microinsurance can be defined as the provision of insurance to low-income households that otherwi... more Microinsurance can be defined as the provision of insurance to low-income households that otherwise do not have access to insurance. It is a natural supplement to microfinance and has the potential of creating a new market for the private sector while complementing the public sector's efforts towards social security for workers in an informal economy. The challenges of microinsurance are manifold. Premium income is low, administrative costs tend to be relatively high, and infrastructure for insurance is lacking. Intimate knowledge of local conditions and requirements is indispensable. The policy-holders are poor and often illiterate people. They often do not dispose over a bank account and may not have a regular income. Therefore, the design of microinsurance products requires innovative solutions regarding distribution channels, premium payments and loss regulation. The design of the policy must be kept as simple as possible. Further on, PML estimates for microinsurance risks a...
Earthquake risk is a function of hazard, vulnerability and values or people at risk. In probabili... more Earthquake risk is a function of hazard, vulnerability and values or people at risk. In probabilistic models designed to assess losses from future earthquakes, the vulnerability of the objects exposed has a dominating influence on the final results because of the wide range of vulnerabilities for different types of risk. The term “type of risk” is often, and especially in the engineering community, understood in the restricted sense of type of (building) construction. In the real risk world, however, building contents, machinery, equipment and consequential losses (loss of production, business interruption) as well as losses from consequential effects (e.g. liquefaction, tsunami) and so-called loss amplification factors (e.g. repair cost inflation) also play an important role, particularly in rare large events. Two approaches are used in vulnerability modelling. First, the empirical method, which is based on loss statistics of past events. Second, a theoretical, engineering-based ap...
Egs General Assembly Conference Abstracts, 2002
ABSTRACT Situated in an active tectonic region the highly industrialised Cologne area (Germany) c... more ABSTRACT Situated in an active tectonic region the highly industrialised Cologne area (Germany) combines a relatively high seismic hazard with a large damage potential. The last ma- jor event in Middle Europe was the Roermond earthquake in 1992 with a Magnitude of Ml=5.9 and the epicentre approximately 70 km north-west of the city of Cologne. The Erft fault system however, having its closest surface exposure only 15 km West of the city, is the most important potential fault system for damaging earthquakes in the region under investigation (Ahorner, 2001, DGG Mittlg., 2, p 3). Being part of the German Research Network for Natural Disasters (DFNK) we aim at integrating geological, geophysical and engineering approaches for the microzona- tion of the Cologne area. Therefore, existing geological data was collected and pro- cessed into a GIS based 3D-model, ambient noise and earthquake recordings were analysed with respect to the resonance frequencies of the soil, ground motion sce- narios were computed using a hybrid modelling approach, and the vulnerability of man-made structures was analysed through finite-element modelling. We show that this integrated approach allows for comparing results coming from dif- ferent methods, improving hereby the existing knowledge of the sub-surface (e.g. thickness of sediments, shear-wave velocity with depth) and the vulnerability anal- ysis of man-made structues. In addition, results can be linked in order to obtain for example the reaction of man-made structures to seismic waves.
Zugl.: Aachen, Techn. Hochsch., Diss., 1994.
Geomechanik und Tunnelbau, 2008
ABSTRACT Loss statistics for natural disasters demonstrate, also after correction for inflation, ... more ABSTRACT Loss statistics for natural disasters demonstrate, also after correction for inflation, a dramatic increase in the loss burden since 1950 which was well confirmed by recent disasters like Hurricane Katrina 2005 and the South Asian tsunami 2004. This increase is driven by a concentration of population and values in urban areas, the development of highly exposed coastal and valley regions, the complexity of modern societies and technologies and probably also by the emerging consequences of global warming. This process will continue unless remedial action is taken. This requires a holistic risk management process which starts with hazard identification and moves on to hazard and risk evaluation. Risk evaluation forms the basis for controlling and financing future losses. Natural disaster insurance plays a key role in this context, but also private parties and governments have to share a part of the risk. A main responsibility of governments is to formulate regulations for building construction and land use. The insurance sector and the state have to act together in order to create incentives for building and business owners to take loss prevention measures.Risikomanagement für Naturgefahren – die Sicht eines globalen RückversicherersSchadenstatistiken für Naturkatastrophen für den Zeitraum seit 1950 zeigen einen dramatischen Anstieg der Schadenlast, auch nach Bereinigung für Inflation. Dieser Trend wurde bestätigt durch Ereignisse wie den Hurrikan Katrina 2005 und den Südasien- Tsunami 2004. Der Anstieg wird im Wesentlichen verursacht durch die Konzentration von Bevölkerung und Werten in Großstadträumen, die fortschreitende Entwicklung hochgefährdeter Küsten- und Talregionen, die komplexe Vernetzung von modernen Gesellschaften und Technologien, und wahrscheinlich auch bereits durch die Folgen der globalen Erwärmung. Dieser Trend wird weiter anhalten, solange nicht entsprechende Gegenmaßnahmen getroffen werden. Gefordert ist dabei ein ganzheitlich angelegter Risikomanagementprozess: Er beginnt mit der Identifikation der relevanten Gefahren und geht über die quantitative Einschätzung der Gefährdung hin zur Risikobewertung. Diese bildet dann die Grundlage für die erfolgreiche Kontrolle und Finanzierung künftiger Schäden. Die Versicherung von Naturgefahren spielt eine Schlüsselrolle für die Finanzierung von Katastrophenschäden, aber auch der private und öffentliche Sektor müssen einen Teil des Risikos tragen. Eine Hauptverantwortung des Staats liegt in der Bereitstellung und Durchsetzung von Bau- und Landnutzungsrichtlinien. Eine gemeinsame Aufgabe von Versicherungssektor und Staat, und von besonderer Bedeutung für die Eingrenzung künftiger Schadenlasten ist die Motivation von privaten und gewerblichen Gebäudeeigentümern zu Maßnahmen der Schadenprävention.
Situated in an active tectonic region the highly industrialised Cologne area (Germany) combines a... more Situated in an active tectonic region the highly industrialised Cologne area (Germany) combines a relatively high seismic hazard with a large damage potential. The last ma- jor event in Middle Europe was the Roermond earthquake in 1992 with a Magnitude of Ml=5.9 and the epicentre approximately 70 km north-west of the city of Cologne. The Erft fault system however, having its closest surface exposure only 15 km West of the city, is the most important potential fault system for damaging earthquakes in the region under investigation (Ahorner, 2001, DGG Mittlg., 2, p 3). Being part of the German Research Network for Natural Disasters (DFNK) we aim at integrating geological, geophysical and engineering approaches for the microzona- tion of the Cologne area. Therefore, existing geological data was collected and pro- cessed into a GIS based 3D-model, ambient noise and earthquake recordings were analysed with respect to the resonance frequencies of the soil, ground motion sce- narios were c...
Earthquake risk is a function of hazard, vulnerability and values or people at risk. In probabili... more Earthquake risk is a function of hazard, vulnerability and values or people at risk. In probabilistic models designed to assess losses from future earthquakes, the vulnerability of the objects exposed has a dominating influence on the final results because of the wide range of vulnerabilities for different types of risk. The term "type of risk" is often understood in the restricted sense of type of (building) construction. In the real risk world, however, building contents, machinery, equipment and consequential losses (e.g. business interruption) also play an important role. Eventually, the prevailing portion of actual monetary earthquake losses are non-structural and contents losses, especially in areas of low seismicity. Although non-structural elements can be modelled in a similar fashion, in the past too much weight has been put on structural losses as compared to other loss components. This introduces further uncertainties in the analysis. In conclusion, the conceptu...
Tectonophysics, 2003
ABSTRACT The Magadi area, located in the southern part of the Kenya Rift, is a seismically active... more ABSTRACT The Magadi area, located in the southern part of the Kenya Rift, is a seismically active region where rifting is still in progress. The recent tectonic activity has been investigated through a seismological survey and the study of neotectonic joints found in Lake Magadi sediments, which were deposited some 5000 years ago. The structural analysis of these open fractures was combined with a quantitative analysis of the orientation and size characteristics of imagery faults. The gathered data demonstrate (1) that the majority of the systematic joints have straight and parallel trajectories with a common en echelon mode of propagation displayed through a rich variety of patterns, and (2) that there is a self-similarity in fault and joint principal directions recognised at the different telescopic scales. SPOT image (1:125,000), aerial photos (1:76,000), and outcrop fieldwork reveal two important structural orientations which are N015°E and N015°W. The N015°E regional direction is consistent with the orientation of the southern segment of the Kenya Rift. Structural analysis is supported by results of a joint microseismic investigation in the Lake Magadi area. Obtained focal mechanism solutions indicate an E–W to ESE–WNW normal faulting extension direction.
Seismological Research Letters, 1999
Natural Hazards, 2006
The study was implemented in the framework of the DFNK (Deutsches Forschungsnetz Naturkatastrophe... more The study was implemented in the framework of the DFNK (Deutsches Forschungsnetz Naturkatastrophen -German Research Network Natural Disasters) project. The area around the city of Cologne was chosen as an object for assessment of seismic hazard and risk. A comprehensive geo-database was compiled for the area, which allows using a computational approach for analysis of site amplification functions and probable surface effects. Taking into account peculiarities of the local soil conditions, the analysis of site effects included both amplification of ground motions and liquefaction potential. These phenomena, having different nature, are interrelated and can considerably contribute to seismic hazard. This paper presents some results obtained on the base of computational analysis using geomodeling.
International Journal of Rock Mechanics and Mining Sciences & Geomechanics Abstracts, 1996
Microinsurance can be defined as the provision of insurance to low-income households that otherwi... more Microinsurance can be defined as the provision of insurance to low-income households that otherwise do not have access to insurance. It is a natural supplement to microfinance and has the potential of creating a new market for the private sector while complementing the public sector's efforts towards social security for workers in an informal economy. The challenges of microinsurance are manifold. Premium income is low, administrative costs tend to be relatively high, and infrastructure for insurance is lacking. Intimate knowledge of local conditions and requirements is indispensable. The policy-holders are poor and often illiterate people. They often do not dispose over a bank account and may not have a regular income. Therefore, the design of microinsurance products requires innovative solutions regarding distribution channels, premium payments and loss regulation. The design of the policy must be kept as simple as possible. Further on, PML estimates for microinsurance risks a...
Geophysical Journal International, 2001
Local seismic activity has been monitored in the southern part of the Kenya Rift in the area arou... more Local seismic activity has been monitored in the southern part of the Kenya Rift in the area around Lake Magadi. An earthquake recording network consisting of 15 station sites was operated for 8 months from November 1997 to June 1998. During this period, the Magadi area proved to be seismically active. Approximately 10 events per day were detected and found to be equally distributed over the rift floor. The hypocentre depth distribution shows surprisingly large depths of up to 27 km in the south and much shallower depths in the northern part of the area. Apart from the background activity, swarm activity with rates of more than 300 events per day was also recorded. The epicentres are clustered and trace a linear structure lying SSW-NNE over a length of 10 km north of Lake Magadi. Hypocentres in the region of the earthquake cluster are shallow and exhibit a sharp cutoff at 9 km depth. A surface crack that occurred during the recording period is connected to the earthquake swarm. Analysis of the focal mechanisms of selected earthquakes indicates predominantly normal faulting in response to a WNW-ESE-directed tensional stress field. This direction corresponds to the general alignment of the southernmost part of the Kenya Rift and to the surface faulting pattern inside the rift. The crustal structure of the area has been investigated using local earthquake tomography and the spatial distribution of hypocentres. The main results of the tomography are a linear positive velocity anomaly following the rift axis and a negative anomaly at shallow depth underneath Lake Magadi. The high velocities can be explained by mafic material that has intruded into the upper crust. The negative anomaly is attributed to highly fractured rocks. Maximum hypocentre depths indicate a body of low shear strength centred at the rift axis and a general deepening of the brittle-ductile transition from north to south.
Geothermics, 1989
Monitoring the natural selsmlcity of Milos island over a four month period led to the conclusion ... more Monitoring the natural selsmlcity of Milos island over a four month period led to the conclusion that the microselamlc activity is concentrated mainly in the central-eastern part of the island In the depth range from 5-8 km. Tomogrsphic inversion of 90 selected events led to a refined veloclty-depth distribution. The fluctuation of velocities appears to be depth-dependent; a remarkable horizontal change of velocities was found for the upper few kllometres of the crust, while at greater depths the crustal velocity is more homogeneous. Minima of the v,Jv=-ratlo coincide with the locations of the production wells in the Zefyrla Plain and close to Adamas, thus indicating higher temperatures in these areas. Faultplane solutions indicate that tensional stress in a NE-SW direction is the actual cause of the seismic activity. The frequency-magnltude relation indicates tectonic activities rather than volcanic.
Disaster Risk …, 2004
The growing loss burden from natural disasters requires a cooperative effort from all parties inv... more The growing loss burden from natural disasters requires a cooperative effort from all parties involved in order to finance, mitigate and reduce the losses from future catastrophic events. The affected stakeholder groups encompass the private sector, i.e. property owners, the financial sector and public authorities, i.e. government bodies on all administrative levels, but also non-governmental institutions and supra-or international organizations. Most important within the financial sector are the insurance and specifically the reinsurance industries, but also banks and the capital market as a whole can play a supportive role in risk financing. Under the heading of "risk partnership" the responsibilities of the persons and entities affected, of the financial sector and the state are described from an international perspective based on actual business practice. It is a challenging task to develop solutions which combine efficient incentives for property owners to undertake risk reduction measures with acceptable and affordable insurance conditions. A close and well-conceived cooperation especially between the state and the insurance sector is indispensable to achieve this goal. Various solutions have been designed and even implemented, but so far none of these have succeeded to a satisfactory degree. The potential role of the insurance sector in risk mitigation is addressed, and some examples of private/public partnerships working in the direction of risk reduction are presented.
Journal of African Earth Sciences, 1998
In 1990 the Geology Department of the University of Nairobi started to build up a seismological n... more In 1990 the Geology Department of the University of Nairobi started to build up a seismological network for Kenya, which has been operating since 1993. In this paper the actual state of this seismological network is described. Additionally, the first results on the seismic activity in the southern part of Kenya and adjacent areas between October 1993 and August 1996 are presented and are compared with historical data. Out of more than 2000 recorded local earthquakes 435 could be localised within the study area with local magnitudes of up to 5. The distribution of the events shows three areas of prominent seismicity: the Rift Valley between Nakuru and northern Tanzania; the area northeast of Kilimanjaro; and the Nyanza Rift in western Kenya. In a first attempt to assess the seismic hazard for the study area, a seismic energy map for the period of observation is given. o 1998 Elsevier Science Limited.
Microinsurance can be defined as the provision of insurance to low-income households that otherwi... more Microinsurance can be defined as the provision of insurance to low-income households that otherwise do not have access to insurance. It is a natural supplement to microfinance and has the potential of creating a new market for the private sector while complementing the public sector's efforts towards social security for workers in an informal economy. The challenges of microinsurance are manifold. Premium income is low, administrative costs tend to be relatively high, and infrastructure for insurance is lacking. Intimate knowledge of local conditions and requirements is indispensable. The policy-holders are poor and often illiterate people. They often do not dispose over a bank account and may not have a regular income. Therefore, the design of microinsurance products requires innovative solutions regarding distribution channels, premium payments and loss regulation. The design of the policy must be kept as simple as possible. Further on, PML estimates for microinsurance risks a...
Earthquake risk is a function of hazard, vulnerability and values or people at risk. In probabili... more Earthquake risk is a function of hazard, vulnerability and values or people at risk. In probabilistic models designed to assess losses from future earthquakes, the vulnerability of the objects exposed has a dominating influence on the final results because of the wide range of vulnerabilities for different types of risk. The term “type of risk” is often, and especially in the engineering community, understood in the restricted sense of type of (building) construction. In the real risk world, however, building contents, machinery, equipment and consequential losses (loss of production, business interruption) as well as losses from consequential effects (e.g. liquefaction, tsunami) and so-called loss amplification factors (e.g. repair cost inflation) also play an important role, particularly in rare large events. Two approaches are used in vulnerability modelling. First, the empirical method, which is based on loss statistics of past events. Second, a theoretical, engineering-based ap...
Egs General Assembly Conference Abstracts, 2002
ABSTRACT Situated in an active tectonic region the highly industrialised Cologne area (Germany) c... more ABSTRACT Situated in an active tectonic region the highly industrialised Cologne area (Germany) combines a relatively high seismic hazard with a large damage potential. The last ma- jor event in Middle Europe was the Roermond earthquake in 1992 with a Magnitude of Ml=5.9 and the epicentre approximately 70 km north-west of the city of Cologne. The Erft fault system however, having its closest surface exposure only 15 km West of the city, is the most important potential fault system for damaging earthquakes in the region under investigation (Ahorner, 2001, DGG Mittlg., 2, p 3). Being part of the German Research Network for Natural Disasters (DFNK) we aim at integrating geological, geophysical and engineering approaches for the microzona- tion of the Cologne area. Therefore, existing geological data was collected and pro- cessed into a GIS based 3D-model, ambient noise and earthquake recordings were analysed with respect to the resonance frequencies of the soil, ground motion sce- narios were computed using a hybrid modelling approach, and the vulnerability of man-made structures was analysed through finite-element modelling. We show that this integrated approach allows for comparing results coming from dif- ferent methods, improving hereby the existing knowledge of the sub-surface (e.g. thickness of sediments, shear-wave velocity with depth) and the vulnerability anal- ysis of man-made structues. In addition, results can be linked in order to obtain for example the reaction of man-made structures to seismic waves.
Zugl.: Aachen, Techn. Hochsch., Diss., 1994.
Geomechanik und Tunnelbau, 2008
ABSTRACT Loss statistics for natural disasters demonstrate, also after correction for inflation, ... more ABSTRACT Loss statistics for natural disasters demonstrate, also after correction for inflation, a dramatic increase in the loss burden since 1950 which was well confirmed by recent disasters like Hurricane Katrina 2005 and the South Asian tsunami 2004. This increase is driven by a concentration of population and values in urban areas, the development of highly exposed coastal and valley regions, the complexity of modern societies and technologies and probably also by the emerging consequences of global warming. This process will continue unless remedial action is taken. This requires a holistic risk management process which starts with hazard identification and moves on to hazard and risk evaluation. Risk evaluation forms the basis for controlling and financing future losses. Natural disaster insurance plays a key role in this context, but also private parties and governments have to share a part of the risk. A main responsibility of governments is to formulate regulations for building construction and land use. The insurance sector and the state have to act together in order to create incentives for building and business owners to take loss prevention measures.Risikomanagement für Naturgefahren – die Sicht eines globalen RückversicherersSchadenstatistiken für Naturkatastrophen für den Zeitraum seit 1950 zeigen einen dramatischen Anstieg der Schadenlast, auch nach Bereinigung für Inflation. Dieser Trend wurde bestätigt durch Ereignisse wie den Hurrikan Katrina 2005 und den Südasien- Tsunami 2004. Der Anstieg wird im Wesentlichen verursacht durch die Konzentration von Bevölkerung und Werten in Großstadträumen, die fortschreitende Entwicklung hochgefährdeter Küsten- und Talregionen, die komplexe Vernetzung von modernen Gesellschaften und Technologien, und wahrscheinlich auch bereits durch die Folgen der globalen Erwärmung. Dieser Trend wird weiter anhalten, solange nicht entsprechende Gegenmaßnahmen getroffen werden. Gefordert ist dabei ein ganzheitlich angelegter Risikomanagementprozess: Er beginnt mit der Identifikation der relevanten Gefahren und geht über die quantitative Einschätzung der Gefährdung hin zur Risikobewertung. Diese bildet dann die Grundlage für die erfolgreiche Kontrolle und Finanzierung künftiger Schäden. Die Versicherung von Naturgefahren spielt eine Schlüsselrolle für die Finanzierung von Katastrophenschäden, aber auch der private und öffentliche Sektor müssen einen Teil des Risikos tragen. Eine Hauptverantwortung des Staats liegt in der Bereitstellung und Durchsetzung von Bau- und Landnutzungsrichtlinien. Eine gemeinsame Aufgabe von Versicherungssektor und Staat, und von besonderer Bedeutung für die Eingrenzung künftiger Schadenlasten ist die Motivation von privaten und gewerblichen Gebäudeeigentümern zu Maßnahmen der Schadenprävention.
Situated in an active tectonic region the highly industrialised Cologne area (Germany) combines a... more Situated in an active tectonic region the highly industrialised Cologne area (Germany) combines a relatively high seismic hazard with a large damage potential. The last ma- jor event in Middle Europe was the Roermond earthquake in 1992 with a Magnitude of Ml=5.9 and the epicentre approximately 70 km north-west of the city of Cologne. The Erft fault system however, having its closest surface exposure only 15 km West of the city, is the most important potential fault system for damaging earthquakes in the region under investigation (Ahorner, 2001, DGG Mittlg., 2, p 3). Being part of the German Research Network for Natural Disasters (DFNK) we aim at integrating geological, geophysical and engineering approaches for the microzona- tion of the Cologne area. Therefore, existing geological data was collected and pro- cessed into a GIS based 3D-model, ambient noise and earthquake recordings were analysed with respect to the resonance frequencies of the soil, ground motion sce- narios were c...
Earthquake risk is a function of hazard, vulnerability and values or people at risk. In probabili... more Earthquake risk is a function of hazard, vulnerability and values or people at risk. In probabilistic models designed to assess losses from future earthquakes, the vulnerability of the objects exposed has a dominating influence on the final results because of the wide range of vulnerabilities for different types of risk. The term "type of risk" is often understood in the restricted sense of type of (building) construction. In the real risk world, however, building contents, machinery, equipment and consequential losses (e.g. business interruption) also play an important role. Eventually, the prevailing portion of actual monetary earthquake losses are non-structural and contents losses, especially in areas of low seismicity. Although non-structural elements can be modelled in a similar fashion, in the past too much weight has been put on structural losses as compared to other loss components. This introduces further uncertainties in the analysis. In conclusion, the conceptu...
Tectonophysics, 2003
ABSTRACT The Magadi area, located in the southern part of the Kenya Rift, is a seismically active... more ABSTRACT The Magadi area, located in the southern part of the Kenya Rift, is a seismically active region where rifting is still in progress. The recent tectonic activity has been investigated through a seismological survey and the study of neotectonic joints found in Lake Magadi sediments, which were deposited some 5000 years ago. The structural analysis of these open fractures was combined with a quantitative analysis of the orientation and size characteristics of imagery faults. The gathered data demonstrate (1) that the majority of the systematic joints have straight and parallel trajectories with a common en echelon mode of propagation displayed through a rich variety of patterns, and (2) that there is a self-similarity in fault and joint principal directions recognised at the different telescopic scales. SPOT image (1:125,000), aerial photos (1:76,000), and outcrop fieldwork reveal two important structural orientations which are N015°E and N015°W. The N015°E regional direction is consistent with the orientation of the southern segment of the Kenya Rift. Structural analysis is supported by results of a joint microseismic investigation in the Lake Magadi area. Obtained focal mechanism solutions indicate an E–W to ESE–WNW normal faulting extension direction.
Seismological Research Letters, 1999
Natural Hazards, 2006
The study was implemented in the framework of the DFNK (Deutsches Forschungsnetz Naturkatastrophe... more The study was implemented in the framework of the DFNK (Deutsches Forschungsnetz Naturkatastrophen -German Research Network Natural Disasters) project. The area around the city of Cologne was chosen as an object for assessment of seismic hazard and risk. A comprehensive geo-database was compiled for the area, which allows using a computational approach for analysis of site amplification functions and probable surface effects. Taking into account peculiarities of the local soil conditions, the analysis of site effects included both amplification of ground motions and liquefaction potential. These phenomena, having different nature, are interrelated and can considerably contribute to seismic hazard. This paper presents some results obtained on the base of computational analysis using geomodeling.
International Journal of Rock Mechanics and Mining Sciences & Geomechanics Abstracts, 1996
Microinsurance can be defined as the provision of insurance to low-income households that otherwi... more Microinsurance can be defined as the provision of insurance to low-income households that otherwise do not have access to insurance. It is a natural supplement to microfinance and has the potential of creating a new market for the private sector while complementing the public sector's efforts towards social security for workers in an informal economy. The challenges of microinsurance are manifold. Premium income is low, administrative costs tend to be relatively high, and infrastructure for insurance is lacking. Intimate knowledge of local conditions and requirements is indispensable. The policy-holders are poor and often illiterate people. They often do not dispose over a bank account and may not have a regular income. Therefore, the design of microinsurance products requires innovative solutions regarding distribution channels, premium payments and loss regulation. The design of the policy must be kept as simple as possible. Further on, PML estimates for microinsurance risks a...