Deterministic Seismic Hazard Analysis Research Articles

Deterministic Seismic Hazard Analysis of Sree Padmanabhaswamy Temple, Kerala State

Deterministic Seismic Hazard Analysis of Sree Padmanabhaswamy Temple, Kerala State

Comparison of peak ground acceleration using deterministic and probabilistic approach in the coastal area of Loh Buaya, Rinca Island, Indonesia

An area located near an active volcano, subduction zone, and/or active fault has a risk of an earthquake. Earthquakes can cause damage to buildings with a large number of losses. One of the earthquake-related parameters required in planning an earthquake-resistant building is the Peak Ground Acceleration (PGA). The objective of this study is to compare the PGA value at the coastal area of Loh Buaya, Rinca Island, Indonesia, using Probabilistic Seismic Hazard Analysis (PSHA) and Deterministic Seismic Hazard Analysis (DSHA). The DSHA is calculated based on earthquake data series from the United States Geological Survey (USGS) in the period between 1922 to 2022. Also, it is calculated using 10 data of Ground Motion Prediction Equation (GMPE). Data from the USGS is constrained with magnitude > 5.0 MW and earthquake distance < 200 km from the study site. The PSHA is based on the Indonesian earthquake hazard map and the de-aggregation map from the National Earthquake Study Centre of Indonesia with a probability exceeding 2% in 50 years. Based on the parameters of PGA maximum, distance, and magnitude, the DSHA by Kanno method has the closest result to the PSHA. It is concluded that this area has a high earthquake risk with a PGA maximum of more than 0.5 g.

Deterministic Seismic Hazard Map Using Region-Specific GMPEs of Maharashtra State, India

Maharashtra stands out as a crucial state in India, demonstrating significant progress in infrastructural development and industrialization. Several prominent cities, including Mumbai, Pune, Nagpur, etc., are significantly contributing to the Indian economy. Considering the importance of the state, a deterministic seismic hazard analysis is executed to reduce the damages to critical and important structures and fatalities caused due to earthquakes. Past earthquakes data are collected within and around the state to prepare a homogenised earthquake catalogue. Seven seismic zones are prepared using K- mean cluster analysis. Independent earthquake events i.e., mainshocks are identified using four renowned declustering methods. Additionally, with the help of mainshocks from each zone, the maximum observed earthquake magnitude ( m^max) and positive correction factor (Δ) are estimated. By superimposing all the mainshocks (after adding Δ) onto the fault map, the maximum observed possible earthquake magnitude of all faults ( M^max) are assigned to each fault. M^max value is used to estimate surface rupture length (RLD) and consecutively, the maximum magnitude (MMax) from fault sources are estimated. Three region-specific ground motion prediction equations (GMPEs) are adopted in the logic trees assigning a proper weightage to each GMPE. A seismic hazard contour maps are prepared at bedrock level, C, and D-type soil sites for Maharashtra. In the western part of the study area, the maximum PGA value is found to be 0.58 g, 0.70 g, and 0.33 g at bedrock level, C, and D-type sites, respectively.

Deterministic seismic hazard analysis from physics-based earthquake simulations in the Eastern Betics (SE Iberia)

The low frequency of large destructive earthquakes in the Eastern Betics (SE Iberian Peninsula), not recorded in the instrumental seismic catalog, complicate the estimation of the maximum ground motion that could be reached. Knowing the characteristics and behavior of these large seismic ruptures is crucial for the study of seismic hazard. In this work, we have used a physics-based earthquake simulator to generate a 100 kyr catalog of seismic ruptures associated with seismogenic faults bordering the quaternary Guadalentin and Bajo Segura basins. From these ruptures, we have selected maximum earthquake scenarios, and those associated with certain probabilities of exceeding a severe magnitude from the synthetic catalog. The estimation of maximum peak accelerations (PGA) by means of ground motion prediction equations include a possible site amplification that we have calculated from a detailed geotechnical classification of soils. According to the simulations, the modeled faults have the capacity to generate maximum earthquakes with magnitudes ranging MW 6.7–7.4. Densely populated urban areas located along the Guadalentin valley, such as Lorca, could be subject to site-dependent PGA values close to 0.6 g on the Alhama de Murcia fault trace. Similar ground motion would affect the coastline of SE Alicante province when evaluating the maximum simulated event in the Bajo Segura offshore fault. But already from magnitudes around MW ∼ 6, PGA estimations exceed critical values of 0.5 g at the south side of the Bajo Segura basin and the city of Murcia, highly dependent of ground-motion amplification induced by thick deposits of very soft and saturated soils. Our scenarios reflect that other factors such as fault geometry, kinematics and the capability observed in the simulations to generate multi-fault ruptures also affect the spatial distribution of maximum ground motion in this region. We expect that this evaluation could contribute as an improvement guideline for future strong motion prediction studies prior to the settlement of new urban infrastructures in the Eastern Betics.

Comprehensive seismic hazard assessment for Guwahati City, Northeast India: Insights from probabilistic and deterministic seismic hazard analysis

This paper presents a comprehensive seismic hazard assessment for Guwahati city, located in the northeast region of India. The earthquake data considered for the study is from 1762 to 2020, which was sourced from the published data of various seismological agencies. The fault information comprises of the latest studies and Seismotectonic Atlas (SEISAT) data. The density of earthquakes close to the faults was used to define the fault zones. The G-R relationship was utilized to calculate the seismicity parameters of the identified faults. We have used PSHA and DSHA to estimate the ground motion parameters such as peak ground acceleration and spectral acceleration at various probabilities of exceedance to calculate the level of seismic hazard. The results indicate that the seismic hazard in Guwahati is moderate to high, with several active faults in the vicinity and a high potential for strong ground motions. This study includes identifying the controlling source for Guwahati and plotting the seismic hazard curve and uniform hazard spectra for various probabilities of exceedance, which will give a basic idea of the seismic hazard of the city. The findings of this study can be used as a basis for earthquake risk reduction and mitigation strategies in Guwahati.

Pemodelan Percepatan Tanah sebagai Parameter Hazard Gempabumi menggunakan Metode Deterministic Seismic Hazard Analysis di Kota Manado

Research has been carried out on modeling ground acceleration as an earthquake hazard parameter in Manado. This study aims to create an earthquake modeling scenario using Deterministic Seismic Hazard Analysis to determine the estimated PGA value and the intensity value of a significant earthquake. This study utilizes the BMKG SHAKEMAP software to determine the PGA value which is then converted into a modified Mercalli intensity value. A total of 13 modeling scenarios were built in this study. The results show that the scenario of significant earthquake modeling in Manado City and its surroundings using the 2018 BMKG catalog input shows varying results. This depends on the earthquake source parameters as well as the distance from the source to the site. Scenario model 10 is the most representative because it has the same intensity value as the June 20, 1991 earthquake. The resulting PGA value shows the area that has the highest PGA in Manado comes from the 3rd model (8.1% g) and the lowest from the model to 12 (1.4 % g). Due to the limited historical intensity data from the catalog, only 8 models out of 13 models were tested for root mean square error verification ranging values from 0 to 0.25.

Quantitative Earthquake Loss Estimates the New Frontier

Abstract Since 2003, an early focus has emerged on estimating earthquake fatalities, injuries, and financial losses. This new inquiry is not yet practiced by a majority of researchers, even though one might argue it is the most important question in seismology today. No sensitive structures like reservoir dams and nuclear power plants could be built without a detailed seismic hazard analysis specifically focused on the site. On the other hand, cities near large active faults do not have their building codes determined by rigorous and specific seismic hazard and risk analyses. This contrast is startling. It seems that where mostly money is at stake, it is mandatory to consider deterministic seismic hazard analyses for construction, whereas where mostly lives are at stake, it is not. I advocate that it should be mandatory for every major city near active faults to have the seismic hazard and risk estimated so as to put an adequate local building code and other safety measures in place. To this end, a standard procedure should be defined to assess local earthquake risk in populated areas exposed to earthquake hazards. In numerous countries, the population numbers in villages, as well as the locations and sizes of schools and hospitals, are not known, and some governments refuse to distribute this information, in spite of the fact that it would be for humanitarian purposes. Because the Open Street Map and Open Building Map begin to cover the globe, this missing information, essential for first responders in natural disasters, will become available and will contribute to preparing populations at risk to reduce the impact of unavoidable future earthquakes.

Seismic Load Design of Rukoh Dam Suppletion Tunnel in Pidie Regency, Aceh, Indonesia, Based on Deterministic and Probabilistic Seismic Hazard Analyses

The Rukoh Dam suppletion tunnel construction site in Pidie Regency, Aceh province, is located 5.6 kilometers from the Seulimeum-South segment of the active Sumatran fault. The active fault features a strike-slip fault mechanism with a slip rate of 7.0 millimeters per year and a maximum earthquake-recorded magnitude of 6.9 Mw. Considering that the construction site is located less than 10 kilometers from the active fault, which may cause earthquakes with a magnitude of at least 6 Mw, the SNI 1729:2019, which describes the procedures for planning earthquake resistance for buildings and non-building structures, requires the seismic load to be designed based on the site-specific responses analysis. Determination of the seismic load using a deterministic seismic hazard analysis was the objective of this study. The seismic load based on the probabilistic seismic hazard analysis by Pusat Studi Gempa Nasional (PusGen) in 2017 is also compared. The 2017 Indonesian Earthquake Source and Hazard Map were used to find out about the fault mechanism, slip rate, deterministic magnitude, orientation, and coordinates of traces. The deterministic seismic hazard analysis was conducted using EZ-FRISK 8.07 software and attenuation equations with shallow crustal earthquake sources for fault and shallow background earthquake sources, i.e., the Boore-Atkinson NGA 2014, the Campbell-Bozorgnia NGA 2014, and the Chiou-Youngs NGA 2014 equations. The deterministic analysis based on those attenuation equations predicted the active fault to result in a peak ground acceleration (PGA) value of 0.66 g at the construction site of the Rukoh Dam suppletion tunnel. In comparison, the probabilistic hazard analysis conducted by Pusat Studi Gempa Nasional (PusGen) in 2017 indicated a peak ground acceleration (PGA) of 0.537 g. Therefore, the seismic load is recommended for the structural designs of the embankment dam and the other infrastructures, particularly the suppletion tunnel.

Ground Motion and Liquefaction Study at Opak River Estuary Bantul

In Mei 2006, an earthquake occurred, and liquefaction was induced in Bantul Regency in the form of lateral spreading and sand boiling. Based on Indonesia’s liquefaction susceptibility zone map 2019, the Bantul coast was identified as a high liquefaction hazard zone. There is a high risk of liquefaction in that location, and if liquefaction occurs, the effective stresses of the soil will be lost. This study aimed to determine ground motion-induced liquefaction potential in Opak river estuary in Bantul. The peak ground acceleration can be predicted by probabilistic seismic hazard analysis (PSHA) based on Indonesian spectra design application, deterministic seismic hazard analysis (DSHA) based on the mechanism of a recent earthquake in Bantul, and non-linear earthquake site response analysis (NERA) based on the 2004 Parkfield California earthquake, the 1986 Chalfant Valley California earthquake, and the 1987 Superstition Hill California earthquake. The value of acceleration from site-specific responses with DSHA and NERA is 0.558 g. Then, the maximum acceleration, seismic magnitude, N-SPT bore log soil, and other soil parameters are analyzed with a semi-empirical simplified method to estimate the safety factor of liquefaction potential using Settle3. The liquefaction safety factor was calculated by dividing the cyclic resistance ratio by the cyclic stress ratio; liquefaction occurs if the safety factor is less than 1. The result indicates that the Opak river estuary has a liquefaction potential beneath the surface from -1.5 to -16.5 m depth with various thick each boreholes. It implies that the bearing capacity design of the foundation system in this area and the liquefaction effect that will emerge when an earthquake occurs must be appropriately considered.

Response Spectrum Design Based on Site Class and Site-Specific Analysis in the Transition Zone

The building structure design needs to pay attention to the seismic code and all its consequences. Building A which will be built in Sleman, Special Region of Yogyakarta is 12.20 km from the Opak Fault causing the Bantul Earthquake of Mw 6.3 in 2006, needs seismic analysis properly using SNI 1726:2019. Based on the site near fault criteria on seismic code, Building A does not belong to the site near fault category, so it used the Probabilistic Seismic Hazard Analysis method. However, considering its distance and magnitude, the value is in the range of the requirements limit. Hence, it is still relevant when compared to the Deterministic Seismic Hazard Analysis method for designing the response spectrum. Based on the site classification in the seismic code, a site that is vulnerable to liquefaction belongs to the site class F and therefore requires site-specific analysis. The site-specific surface response spectrum is taken from the equivalent-linear and non-linear site response analysis using Deepsoil v7.0 software. The response spectrum is also calculated based on site class according to the shear wave velocity (v s) and N-SPT criteria. The site-specific spectral acceleration results are compared to 80% of the site class E spectral acceleration, as required. The site belongs to site class D using v s criteria and belongs to site class E using the N-SPT criteria. Only the equivalent-linear site response spectrum in the modified maximum horizontal direction spectrum is eligible when compared to requirements. Most of the non-linear site response spectrum results or the geometric mean response spectrum of the equivalent-linear site response results can satisfy the requirements compared to 80% of the site class D spectral acceleration because the site response analysis uses the v s parameter. The non-linear site response spectral acceleration is smaller than the equivalent-linear site response spectral acceleration.

Seismic hazard analysis using Deterministic Seismic Hazard Analysis (DSHA) Method: A case study in Southern Malang District, East Java

Indonesia is a country that has a high earthquake threat. The United States Geological Survey (USGS) recorded that Indonesia experienced 5,439 earthquakes with a magnitude of Mw 5. Geologically, Indonesia is located about 200 km from the subduction zone of the Indo-Australian and Eurasian plates. Malang Regency faces the subduction of the Indo-Australian and Eurasian plates. Earthquakes that occur in plate subduction areas will propagate in various directions, including to Malang Regency. Thus, Malang Regency, especially in the southern part, has a high earthquake threat. This study aims to calculate the earthquake threat using a deterministic approach. Earthquake threats can be calculated using the Deterministic Seismic Hazard Analysis (DSHA) method. This study obtained the Mc. Guirre and Donovan attenuation function. These two attenuation functions produce different Peak Ground Acceleration values. The calculations with the Mc. Guirre attenuation function has a range of PGA values from 38,76461 gals to 69,78215 gals. Meanwhile, the Donovan attenuation function calculation produces a range of PGA values from 41.97550 gals to 76.21376 gals. Based on the value of ground acceleration during an earthquake, Bantur, Gedangan, and Sumbermanjing sub-districts are the sub-districts with the highest earthquake threat level in Southern Malang Regency. Tirtoyudo Village, Tirtoyudo District, Malang District has a lower PGA value when compared to Gedangan District. However, the amount of damage to buildings in this subdistrict was much higher. Since the building structure in Tirtoyudo Village cannot withstand ground shaking due to the earthquake, there is damage to the structure of the building.

Structural evaluation of existing buildings using surface ground motions

Research on new seismic sources and seismic data has already performed in 2016 to 2017. Four new shallow crustal fault sources were observed surrounding the city of Semarang, the capital city of Central Java Province, Indonesia. The seismic parameters related with the seismic mechanism (reverse fault) and the maximum magnitude prediction (6.5 Mw) for each seismic sources was also released based on the 2017 research. Following this research, structural evaluation especially for buildings that was designed and constructed based on 2002 Indonesian Seismic Code was also performed. The spectral acceleration design of 2002 seismic code was developed based on subduction source located at the southern of Java island. The structural evaluation was performed for all university buildings located at the Diponegoro University. This paper describes the seismic hazard analysis results of the university area and an example results of building evaluation located at this area. The seismic hazard analysis was performed based on the 2002 Probability Seismic Hazard Analysis/PSHA of the code and the Deterministic Seismic Hazard Analysis (DSHA) of four seismic sources. Two different structural analysis were conducted for all buildings such as structural deformation and drift ratios. Based on the seismic hazard analysis results, all buildings located at the university area were strong enough in resisting the surface ground motion (Peak Ground Acceleration/PGA) due to shallow crustal fault earthquake scenarios having magnitude 6.5 Mw. The buildings deformation and drift ratios calculated using 2002 Indonesian seismic code are greater compared to the same analysis calculated based on deterministic model of shallow crustal fault sources.

Earthquake Damage Assessment of Buried Pipeline Networks in the Lima Metropolitan Area

Lifelines such as drinking water and sewage systems provide the means and conveyance for daily critical services, and they are essential systems for recovery operations after a damaging earthquake. Therefore, earthquake damage to lifeline components needs to be reliably assessed for a possible future seismic scenario. This study presents an earthquake damage assessment of buried pipeline networks in the Lima Metropolitan Area (LMA). It includes seismic hazard analysis, a review of pipeline network datasets, and the selection of empirical fragility functions. Deterministic seismic hazard analysis was performed for an inter-plate earthquake scenario using ground motion prediction equations and site conditions to compute the distribution of the peak ground velocity (PGV). Recommendations are offered for an adequate selection of fragility functions developed in other regions, and a logic tree of fragility functions is proposed to be used in pipelines of LMA according to the data of pipeline damage after the 2007 Pisco Earthquake. Finally, the pipeline repair ratios and the total number of repairs are estimated for the earthquake scenario, and the results are geographically presented for each pipeline network.

The Study of Seismic Hazard in Near-Fault Areas Using Probabilistic and Deterministic Approach

Earthquake is one of the most common natural disasters in Indonesia and usually destroys both high and low-rise buildings as well as triggers liquefaction and Tsunami. This means it is important to provide a robust building design with the ability to resist earthquake load and other induced phenomena. One of the methods commonly used to determine the relevant response spectrum of the bedrock is seismic hazard analysis which can be either Probabilistic Seismic Hazard Analysis (PSHA) or Deterministic Seismic Hazard Analysis (DSHA). The application of PSHA allows the representation of the response spectrum of an earthquake using the return period, thereby providing the engineers with the flexibility of selecting the appropriate natural period. Meanwhile, DSHA is based on geological observations and empirical data that can be easily understood. This research discussed the greater influence of seismic hazard analysis on the bedrock response spectrum of near-fault areas including Bandung situated at a distance of 12.9 km from Lembang Fault, Palu at 3 km from Palu Fault, and Yogyakarta at 8.5 km from Opak Fault. Moreover, EZFRISK Program was used to generate a response spectrum at bedrock and the results showed that PSHA is consistently more conservative than DSHA. It was also noted that there are significant differences at shorter periods for Palu site but these differences were observed at the natural period between 1s and 2s for Bandung and Yogyakarta sites.

Deterministic Seismic Hazard Analysis to Determine Liquefaction Potential Due to Earthquake

The great rocking of building structures and the occurrence of liquefaction in water-saturated soil on river banks are generally caused by earthquake shaking. The waves generated by the earthquake are the main cause of the shaking. In order to show the effect of ground motion earthquake shaking on the response of structures and liquefaction processes, it is necessary to analyze the structure and liquefaction as well as the time history of artificial earthquake ground motions. An artificial time history for liquefaction analysis can be developed based on spectral matching to the target spectrum generated by a deterministic seismic hazard analysis. Therefore, the time history recovered from the analysis can be said to be derived from a deterministic procedure. The analysis of liquefaction with time history aims to see the potential for liquefaction in the Palu region of Central Sulawesi by developing the time history of the bedrock. The time history of the bedrock is then spread over the ground surface. The propagation of time-historical waves to the ground surface can cause liquefaction events in the soil layer. It was found that liquefaction occurred in the Palu region, especially in the Anutapura Hospital building. No other liquefaction potential analysis studies were found in the region. Doi: 10.28991/CEJ-2023-09-05-012 Full Text: PDF

Behaviour of Precariously Balanced Rocks under Seismic Excitation

A naturally occurring geological formation is precariously balanced rocks (PBRs) which might easily topple by an earthquake with severe ground motion. These rocks have been at the same place for many years. Strong ground accelerations have not occurred in the area for thousands of years as shown by the zone of unstable rocks. So, they are significant in both the engineering and seismological domains since they provide source of data for the maximum earthquake ground motion occurring at a site over the rock’s life time. The precariously balanced rock taken for this study is Krishna Butter Ball which is in Mahabalipuram, Chengalpattu district. In the numerical analysis, the peak ground acceleration at which the Krishna butter ball may topple is obtained. To identify the possible future earthquake, deterministic seismic hazard analysis has been carried out for Chengalpattu district. For this analysis, fault details have been obtained from Geological Survey of India. Arc map 10.1 version in Geographical Information System (GIS) platform is used for the interpretation of data like fault length, source (fault) to site (Mahabalipuram) distance from the fault details given by GSI. From the results of Deterministic Seismic Hazard Analysis (DSHA), it is observed that the possible future earthquake may have the magnitude in the range of 6.03 to 7.9. The computed peak ground acceleration (PGA) value corresponding to those magnitude ranges from 0.027g to 0.49g. The maximum PGA value 0.49g corresponds to the Palar river fault which is just 28.53 km away from the Krishna butter ball. From the results of numerical analysis, the behavior of Krishna butter ball for three different PGA i.e. 0.05g, 0.1g, 0.15g has been observed. Newmark sliding block analysis said that the rock may topple at the PGA of 0.35g. From this it can be concluded that the toppling acceleration of Krishna butter ball is relatively low.

Analysis of liquefaction potential in Opak Fault nearby area (case study: Solo-Yogyakarta-NYIA Kulon Progo Toll Road construction section I.2)

Construction of the Solo – Yogyakarta – NYIA Kulon Progo Toll Road Section I.2 is a part of Java's toll road network system that connects Solo and Yogyakarta. The presence of this opak fault allegedly cut the toll road alignment. Based on Indonesia's Liquefaction Vulnerability Zone Map, the alignment location is in a medium liquefaction vulnerability zone. This study aims to determine the potential of liquefaction in the construction of Solo – Yogyakarta – NYIA Kulon Progo Toll Road Section I.2 (stationing 29+000 - 36+000). The maximum peak ground acceleration on the surface was calculated using the Deterministic Seismic Hazard Analysis calculation. Calculating liquefaction potential analysis uses the simplified procedure method developed by Idriss and Boulanger. The research shows that ten borehole points with sandy soil types 2 m – 18 m below the surface have liquefaction potential. The depth of the groundwater table is between 0.2 m – 10 m below the ground surface. Based on the Liquefaction Potential Index analysis, the research location is in a low - high level of liquefaction vulnerability.

Deterministic seismic hazard analysis for Phuentsholing region of southern Bhutan considering local site effects

Deterministic seismic hazard analysis for Phuentsholing region of southern Bhutan considering local site effects

Seismic hazard analysis for engineering sites based on the stochastic finite-fault method

Seismic hazard analyses are mainly performed using either deterministic or probabilistic methods. However, there are still some defects in these statistical model-based approaches for regional seismic risk assessment affected by the near-field of large earthquakes. Therefore, we established a deterministic seismic hazard analysis method that can characterize the entire process of ground motion propagation based on stochastic finite-fault simulation, and we chose the site of the Xiluodu dam to demonstrate the method. This method can characterize earthquake source properties more realistically than other methods and consider factors such as the path and site attenuation of seismic waves. It also has high computational efficiency and is convenient for engineering applications. We first analyzed the complexity of seismogenic structures in the Xiluodu dam site area, and then an evaluation system for ground motion parameters that considers various uncertainties is constructed based on a stochastic finite-fault simulation. Finally, we assessed the seismic hazard of the dam site area comprehensively. The proposed method was able to take into account the complexity of the seismogenic structures affecting the dam site and provide multi-level parameter evaluation results corresponding to different risk levels. These results can be used to construct a dam safety assessment system of an earthquake in advance that provides technical support for rapidly and accurately assessing the post-earthquake damage state of a dam, thus determining the influence of an earthquake on dam safety and mitigating the risk of potential secondary disasters.

Spatial and Temporal Distribution of Lobate Scarps in the Lunar South Polar Region: Evidence for Latitudinal Variation of Scarp Geometry, Kinematics and Formation Ages, Neo‐Tectonic Activity and Sources of Potential Seismic Risks at the Artemis Candidate Landing Regions

AbstractLobate scarps (thrust faults) in the lunar south polar region (90°–60°S) provide important insights into tectonic history, seismicity, and seismic hazard potential of landing sites. In this study, we discovered 75 new lobate scarps and &gt;500 segments, exhibiting latitudinal variation of geometry and movement directions. Formation ages of 141 prominent scarp segments show fault growth rates and directions, decreasing ages from south pole to mid‐latitude, continuous tectonic activity in the last 100 million years with a peak around 10 Ma, seismic resetting of ages, and timings of global contraction. The scarps are capable of producing small‐medium size moonquakes within 5–10 km depths. The deterministic seismic hazard analysis, considering occurrence of MW 1–4 shallow moonquakes along the scarps in the next few decades, and their seismic ground motion characteristics, suggests variable levels of potential seismic risk at the Artemis candidate landing regions and further probabilistic seismic hazard analysis is necessary.