**4. Urban earthquake risk**

422 Earthquake Research and Analysis – Statistical Studies, Observations and Planning

consolidation problems. Land use decisions as the selection of multi-storey building, medium storey building, low rise building, open green areas and industrial use areas, when considered with ground properties, one area that is not suitable for one use do not necessarily have the risk for some other use. For instance, a swampy area that is not suitable for the construction of multistorey building can satisfy the requirement for open

As for topographic threshold, with the increase of slope habitability and the cost increases. Rough topography urges the urban design, construction layout, building type and structuring requirements. While 15% of slope in settlement increases the cost, the slope over 30% results in serious technical infrastructure problems. On the other hand, the slope under

In an urban area with earthquake hazard risk, earthquake analysis should have the priority and the directive role. The detail and the qualification of the analysis and synthesis before planning exhibit variability from upper scale studies to subscales ones. In urban settlements and development areas, the distance to the fault, the features of the ground, topographic factors, liquifaction requirements, landslides and floods as secondary threats, the ratio of fullness and emptiness, the selection of open green area should be analyzed. Structural order, structuring requirements should be arranged in a way that the effects of probable earthquake are prevented. In order not to have resonance, the interaction of soil and structure and the vibrational periods should be evaluated well. The selection of technology and material that control the building quality should be determined considering the soil

In urban design and settlement, prevailing wind direction and insolation are very important. In settlement pattern there should have air corridors to reach all buildings and buildings should be designed in a way that does not interrupt others's light. As for the site selection for the industry, similarly, prevailing wind direction is very important in the sense that spreading malodor to the city and air pollution. Besides, in rainy regions, the risk of flooding should be taken into account and flood risk analysis should be conducted. At the regions under risk, appropriate precautions (correcting the stream beds, leaving the stream beds for open space arrangements rather than opening those to the settlement) should be taken. Moreover, climate properties also affect the foundation type and depth regarding the

Ecological values are destroyed with the effects of urban development and the natural balance is degenerated. Therefore, in any kind of habitability analysis natural balance

Urban development areas should be in relation with the current land use. The current transportation and infrastructure system, social equipment, commerce and important centers of the cities should be associated with new subcenter and settlement units. A settlement pattern disconnected from the current city will have difficulty in supplying the

Geoenvironmental and urban thresholds, after evaluated one by one and their priorities and the weights calculated by statistical methods (MCDA, MCDSS, GisVBA, AHP, Grey relation analyses etc.), are superposed with the maps showing natural and human activity thresholds and in final synthesis map the remaining areas out of the thresholds are defined as the urban development directions. Afterwards, the decisions on urban use areas (residential, commercial or industrial) are given in line with threshold analysis and cost

should be taken into consideration and the living habitats should be protected.

green area arrangement.

5% creates drainage problems.

condition and seismicity.

settlement.

analysis.

needs and developing.

In the settlements with earthquake risk, for the determination of urban risks geological data analysis is not sufficient alone. Building stock and quality in the urban area and the authentic nature of urban texture are also important factors in the evaluation of the earthquake effects. Therefore, while the urban risk analyses are conducted, all the parameters based on the current settlement quality and features, concentration, equipments, infrastructure and transportation networks should be included in the analyses.

Hazard mitigation studies before an earthquake is the most significant stage of disaster preparation process. In this process, the determination of the primary risks and the corresponding precautions for these risks decrease the life and monetory losses during an earthquake. The first step of the determination of the risks at urban areas is to understand the soil behavior that the city rests on by investigations. Besides, the identification of the building quality of the building stock and the revealing of the soil-structure interaction define the type and the approach of the precautions. New settlements are to be realized under the light of the geological data of the city. The inputs of geological data into the planning and design scale play an effective role in the reduction of urban risks. However, these data should be simple enough for planners and designers so that they are understood and implemented. The accurate use and the synthesis of those data banks are of prime importance in understanding the behavior of earthquakes on urban elements. These data providing inputs for architecture, planning and design shape the city. It is an indispensible necessity that in the creation process of earthquake resistant sustainable cities, geology, planning, architecture and design disciplines work together in a way developing a common terminology.

The risk level of the city changes with the population density, building quality, local ground conditions and distance to fault line. The city is subjected to one single earthquake magnitude and threat, however, settlement units that constitutes the city are faced to different levels of urban risks. The resistance of the settlements that have high quality and earthquake resistant buildings resting on hard soil to the same magnitude earthquake, certainly, will be higher than that of ordinarily constructed areas on problematic and loose soil conditions (Figure 4) due to their geotechnical properties. Therefore, the former will have less urban risks. In other words, in urban areas buildings are constructed with different materials in different structural systems and they can be newly constructed or already completed the economic life. Therefore, at the instant of the earthquake the reaction of the building and the extent of the damage will be controlled by the structural features and the geotechnical characteristics of the ground.

In earthquake prone areas, the effect of earthquake waves on the ground, how this effect is reflected to the building and the reaction of the building to this effect should be clarified in an accurate way by interdisciplinary work. These valuable data obtained by experimental analysis, synthesis and calculations help to the determination of the precautions against urban risks. These precautions can be as strengthening of the buildings or evacuation of weak buildings or abandoning of the settlement area before the earthquake during the stage of hazard mitigation as well as the providing of the transportation of the aids in emergency and constructions after earthquakes through a short and alternative routes and the determination of the regions of emergency action.

Correlation Between Geology, Earthquake and Urban Planning 425

Fig. 5. An example of faulting on North Anotolian Fault Zone in Turkey. It is taken from

Fig. 6. An example of rockfall. It is taken from USGS (US Geological Survey) website.

Photographer is unknown.

USGS (US Geological Survey) website. Photographer is unknown.

Fig. 4. An example of loose soil in Adapazar after 1999 Marmara earthquake. It is taken from http://avnidincer.8m.com/depfoto.html. Photographer is Eşref Yalçnkaya.

Therefore, urban earthquake risks, essentially, result from the geological, geotechnical characteristics of the ground, tectonism of the region and the relation of settlement area with active faults, soil-structure interaction and topography of the city. These risks, in the soil, can be observed as faulting (Figure 5), settling-consolidation, slipping, liquefaction, land slide, rock fall (Figure 6) etc. The most important risks due to soil-structure interaction are that resonance causing the collapse (prevailing natural period of the building being equal to that of the soil) and soil amplification. The velocity of the earthquakes waves in the soil changes with the hardness and the properties of the soil. For instance, the waves passing through a hard rock mass pass very quickly and the quake is less felt due to the firmness and the voidless nature of the rock while those passing through loose and weak ground pass very slowly filling the voids in the ground and result in the severe feeling of the quake. This behavior of the soil is defined as soil amplification. Therefore, soil amplification factor of alluvial material, which is higher than that of the rock, causes the strong quaking on the alluvial settlement areas with high rate of damage while that of granite will empower the settlement above it.

Fig. 4. An example of loose soil in Adapazar after 1999 Marmara earthquake. It is taken from http://avnidincer.8m.com/depfoto.html. Photographer is Eşref Yalçnkaya.

settlement above it.

Therefore, urban earthquake risks, essentially, result from the geological, geotechnical characteristics of the ground, tectonism of the region and the relation of settlement area with active faults, soil-structure interaction and topography of the city. These risks, in the soil, can be observed as faulting (Figure 5), settling-consolidation, slipping, liquefaction, land slide, rock fall (Figure 6) etc. The most important risks due to soil-structure interaction are that resonance causing the collapse (prevailing natural period of the building being equal to that of the soil) and soil amplification. The velocity of the earthquakes waves in the soil changes with the hardness and the properties of the soil. For instance, the waves passing through a hard rock mass pass very quickly and the quake is less felt due to the firmness and the voidless nature of the rock while those passing through loose and weak ground pass very slowly filling the voids in the ground and result in the severe feeling of the quake. This behavior of the soil is defined as soil amplification. Therefore, soil amplification factor of alluvial material, which is higher than that of the rock, causes the strong quaking on the alluvial settlement areas with high rate of damage while that of granite will empower the

Fig. 5. An example of faulting on North Anotolian Fault Zone in Turkey. It is taken from USGS (US Geological Survey) website. Photographer is unknown.

Fig. 6. An example of rockfall. It is taken from USGS (US Geological Survey) website. Photographer is unknown.

Correlation Between Geology, Earthquake and Urban Planning 427

Fig. 7b. An example of landslide in Laguna Beach, Bluebird Canyon, California .

Survey). Photographer is Jim Budak.

(Figure 7b) areas that are prone to landslides.

collapse and subsidence risk (Figure 8b).

main actors of decision process.

decisions.

It was devoloped in steep and high slope. It is taken from USGS website (US Geological

regardless of its being on the fault line while the buildings on filled soil far from the fault line collapse. For that reason, in the spatial plans made in earthquake regions with hard topography, it should be avoided to settle on the valley plains (Figure 7a) and high slope

The liquefaction is a geologic hazard that occurs in the grounds that are cohesionless and have underground water and if it occurred in the settlement area, it is an urban risk (Figure 8a, b). On the soil that the building rest on, soil-water mixture moving with liquefaction creates deep enormous voids under the buildings (Figure 8a). That results in the subsidence or the overturning of the building. Especially, the buildings constructed very closed to the sea on the sand soil when they are under seismic excitation have the serious risk of urban

As seen, in the site selection, land use, urban planning and design, geological data are the

During an earthquake, besides the geologic hazards, planning and design errors as wrong site selection, wrong land use decisions, urban uses off the objective, error regarding the design, insufficiency of infrastructure, low building quality give rise to the serious urban risks. For that reason while taking the precautions for the mitigation of the hazard before earthquake not only risks from the geologic thresholds but also analysis, synthesis and evaluations regarding all spatial criteria as macroform of the city, design, urban equipment, concentrations etc should be done and urban risks should be reflected on plan

The closeness to the fault in settlements is not a sole requirement, although it is very important, in the development of urban risks. Certainly, the constructions on the active fault line will feel the quaking more than others. However, the earthquake experiences in the world and in Turkey showed that strong building resting on hard soil could stand

Fig. 7a. An example of landslide. It was devoloped in valley plains. It is taken from http://www.harikasozler.net/img3851.htm. Photographer is unknown.

The closeness to the fault in settlements is not a sole requirement, although it is very important, in the development of urban risks. Certainly, the constructions on the active fault line will feel the quaking more than others. However, the earthquake experiences in the world and in Turkey showed that strong building resting on hard soil could stand

Fig. 7a. An example of landslide. It was devoloped in valley plains. It is taken from

http://www.harikasozler.net/img3851.htm. Photographer is unknown.

Fig. 7b. An example of landslide in Laguna Beach, Bluebird Canyon, California . It was devoloped in steep and high slope. It is taken from USGS website (US Geological Survey). Photographer is Jim Budak.

regardless of its being on the fault line while the buildings on filled soil far from the fault line collapse. For that reason, in the spatial plans made in earthquake regions with hard topography, it should be avoided to settle on the valley plains (Figure 7a) and high slope (Figure 7b) areas that are prone to landslides.

The liquefaction is a geologic hazard that occurs in the grounds that are cohesionless and have underground water and if it occurred in the settlement area, it is an urban risk (Figure 8a, b). On the soil that the building rest on, soil-water mixture moving with liquefaction creates deep enormous voids under the buildings (Figure 8a). That results in the subsidence or the overturning of the building. Especially, the buildings constructed very closed to the sea on the sand soil when they are under seismic excitation have the serious risk of urban collapse and subsidence risk (Figure 8b).

As seen, in the site selection, land use, urban planning and design, geological data are the main actors of decision process.

During an earthquake, besides the geologic hazards, planning and design errors as wrong site selection, wrong land use decisions, urban uses off the objective, error regarding the design, insufficiency of infrastructure, low building quality give rise to the serious urban risks. For that reason while taking the precautions for the mitigation of the hazard before earthquake not only risks from the geologic thresholds but also analysis, synthesis and evaluations regarding all spatial criteria as macroform of the city, design, urban equipment, concentrations etc should be done and urban risks should be reflected on plan decisions.

Correlation Between Geology, Earthquake and Urban Planning 429

Tam (2010) defined the earthquake sensitive planning as an integrated planning which aims to mitigate the earthquake risk factor by considering the physical properties and socioeconomic structure of the settlements and which starts from upper scales and develops socioeconomical development policies and supra-national, national and regional plans to further continue to local planning and subscales in which the progressive synergy is

Earthquake sensitive planning is a planning action that primarily analyzes the earthquake hazard and risks in the planning, prevents these risks and hazards to turn into disasters, internalizes the planning to mitigate earthquake hazards and urban design approaches. The main approach of earthquake sensitive planning is to include the risk mitigation precautions of all disciplines related to earthquake in the planning process for the realization of urban

Earthquake sensitive planning includes the evaluation of geologic hazards and restrictions as risk factors in planning process and their reflection in planning decisions. Within this context, in planning the use of geological data should be assured and regarding the earthquake sensitive planning for hazard mitigation and prevention policies and

The process of building earthquake resistant cities comprises the analysis of geoenvironmental natural hazards that can be occurred during an earthquake or after it, the evaluation of the damage assessment and the revealing the corresponding urban mistakes and the conduction of urban risk analyses. Besides, earthquake sensitive planning approach should be developed to eliminate the risk factors due to land use, site selection, settlement

Earthquake sensitive planning is a dynamic action that zooms out urban planning from the spatial design based traditional planning approach, integrates the risk mitigation precautions in the planning process and incorporates the detailed microzoning maps that go

Earthquake sensitive planning involves an analysis perspective starting from the world scale to national, regional, urban and local scale which covers the small settlement units. This perspective bases on the physical, economical and social development and urban risk

In every stage of this planning approach, geoenvironmental hazard and risk factor should be determined by geological-geotechnical investigation and microzoning maps and with

For the reduction of urban risks and hazard, potential development areas with alternatives developed for physical plans by the directive of the geological data should be selected by using the multi decision analysis techniques as well as with the inclusion of socioeconomic

In earthquake sensitive planning, the interpretations on the analysis of geoenvironmental thresholds and their implementation on the plan are discussed above in the section "Earthquake as planning threshold". In the case where the macroform of the city, layout and socioeconomic development are taken into account, the required action that should be

1. Engineering structures like highway, railway, viaduct, tunnel and construction layout should not intersect the fault line perpendicularly. In the cases where the development

this geological data analysis there should made feedbacks in every planning stage.

considered in earthquake sensitive approach can be listed as follows:

planning that provides healthy, reliable, livable urban environment development.

**5. Earthquake sensitive planning** 

assured. (Reference: Deniz Tam)

approaches should be developed.

pattern and the structuring.

analyses.

beyond the standard geological investigations.

analysis under the earthquake scenarios.

Fig. 8a. An example of liquefaction in TURKEY after 1999 Marmara Earthquake. It is taken from http://www.el-aziz.net/img4381.htm. Photographer is unknown.

Fig. 8b. An example of liquefaction in TURKEY after 1999 Marmara Earthquake. It is taken from http://www.kenthaber.com/marmara/kocaeli/Haber/Genel/Normal/depremdeyikilan-konuta-imza-atti/3d13f1c8-4158-4ce1-b380-13e53de1be21. Photographer is unknown.
