Time-dependent Seismic Hazard Research Articles

Gaussian process regression driven rapid life-cycle based seismic fragility and risk assessment of laminated rubber bearings supported highway bridges subjected to multiple uncertainty sources

Structural attributes, corrosion of steel rebars in reinforced concrete (RC) columns, thermal oxidative aging of inherent rubber in laminated rubber bearings (LRBs), replacement of LRBs, and the time-dependent seismic hazard level at the bridge site are well recognized as the main factors that affect the accurate assessment of the seismic performance of RC bridges implemented with LRBs. However, the probabilistic seismic demand model (PSDM) and probabilistic structural capacity model (PSCM) of deteriorated bridge components may not exhibit homoscedastic log-linearity. And the expansion of seismic fragility surfaces and seismic risk curves in the temporal dimension requires a considerable computational cost on the nonlinear analysis, which regretfully has not been well addressed in current studies. To fill in this gap, this study proposes a life-cycle based seismic fragility and risk assessment framework for LRBs supported RC bridges considering deterioration mechanisms of bridge components during their life cycles demonstrated by a three-span LRBs supported highway bridge considering multiple uncertainties such as the replacement interval for LRBs. In this framework, Gaussian process regression (GPR) is employed to effectively construct the PSDM and PSCM of deteriorated bridge components, and then the time-dependent seismic fragility surfaces of bridge components and bridge system are established. Life-cycle based seismic risk analysis is conducted to quantify the coupled time-dependent effects of deterioration and site seismic hazard on a newly built bridge during its design service life and a deteriorated bridge within its remaining service life, respectively. Results indicate that GPR can successfully capture the nonlinearity and heteroscedasticity characteristics of PSDM and PSCM, leading to a significant reduced number of nonlinear analysis cases to generate the time-dependent seismic fragility surfaces and seismic risk curves. Consequently, the proposed framework using GPR can significantly improve the accuracy and efficiency of life-cycle based seismic performance assessment when uncertainties of structural attributes, deterioration progress and seismic hazard are taken into consideration.

One tune, many tempos: Faults trade off slip in time and space to accommodate relative plate motions

Analysis of incremental slip rates from the four major strike-slip faults of the Marlborough fault system (MFS) of northern South Island, New Zealand, provides a first-ever record at the scale of an entire plate-boundary fault system of how relative plate motions are accommodated in time and space. This record, which spans the past 350–450 m of relative plate motion and ca. 12–14 ky, demonstrates that the fault system as a whole accommodates a steady plate-boundary slip rate, with the MFS faults “keeping up” with the overall rate of relative Pacific-Australia plate motion at relatively short displacement (10 s of meters) and time (102–103 yr) scales. These results affirm the often-assumed but until now unproven assumption that the relative plate-motion rate provides a robust basic constraint on both geodynamical models and analyses of system-level seismic hazard at these scales. In marked contrast, the incremental slip rates of each of the four main Marlborough faults are highly variable through time, marked by coordinated accelerations and decelerations spanning 4–6 earthquakes and several millennia as the faults trade off slip to accommodate a steady relative plate motion rate. These results suggest that (a) the weakest fault in the system will slip faster than average while adjacent mechanically complementary faults slip more slowly, and (b) that these patterns switch back and forth through time, likely reflecting reversible changes in the strength (i.e., resistance to shear) of the individual faults as they collectively accommodate relative plate motion. Interestingly, the periods of fast slip on the MFS faults exhibit ∼20–25 m of displacement, suggesting that these may record periods of fast slip on a weakened fault/ductile shear zone that continues until it uses up all locally stored elastic strain energy, thus potentially approaching local complete stress drop, albeit during a few tens of meters of rapid fault slip during multiple earthquakes, rather than during a single event. This hypothesis is consistent with typical earthquake stress drops of ∼1–10 MPa and estimates of depth-averaged crustal shear stress of a few 10 s of MPa, such as might be released in clusters of 4–6 earthquakes. These results emphasize the need to analyze the collective behavior of the entire fault systems, rather than just individual faults, to understand the mechanics of the system. Moreover, these patterns suggest a potential path forward for more accurate estimation of time-dependent seismic hazard, with the possible incorporation of current position of a fault within a fast- or slow/no-slip period into the probability analysis, as well as a means of potentially estimating crustal shear stress.

Nearby fault interaction within the double-vergence suture in eastern Taiwan during the 2022 Chihshang earthquake sequence

Nearby faults interact through stress changes induced by fault slip and viscoelastic flow. The process is, however, often elusive and can be geometry-dependent and time-variant. Here, we combine geodetic and field observations to characterize the interaction of two head-to-head, conjugate faults in eastern Taiwan during the 2022 Chihshang earthquake sequence. We map the coseismic slip on the Central Range fault and dynamically-triggered shallow slip on the Longitudinal Valley fault, which has been creeping interseismically. Overlapping of seismic and aseismic slip suggests that the Longitudinal Valley fault is capable of hosting a variety of distinct slip behaviors. Moreover, substantial slip on the Central Range fault suppresses Coulomb stress on the Longitudinal Valley fault, and vice versa, resulting in seismic bursts in an out-of-phase pattern on the two faults as seen in the hundred-year historical records. Such fault interaction implies the need for time-dependent seismic hazard reassessment for the complex fault system.

A time-dependent seismic hazard model following the Kaikōura M7.8 earthquake

ABSTRACT Following the 2016 M7.8 Kaikōura earthquake, a time-varying seismic hazard model (KSHM) was developed to inform decision-making for the reinstatement of road and rail networks in the northern South Island. The source model is the sum of a gridded 100-year earthquake clustering model and an updated fault source model. The gridded model comprises long-term, medium-term and short-term components. The 100-year gridded model is constructed as the sum of 100 annual forecasts. A discounting method trades off expected earthquake occurrences of the distant future against those of the near future. The fault source model includes updates to account for newly revealed faults that ruptured in the Kaikōura earthquake and other recently obtained new information, and new time-varying probabilities of rupture for four fault segments. Two different characterisations of the Hikurangi subduction interface are incorporated via a logic tree, with weights determined by an expert panel. A suite of ground motion prediction equations contribute to a logic tree in order to account for epistemic uncertainties in source modelling for each of four tectonic region types. Here, we compare the resulting hazard estimates with the 2010 National Seismic hazard Model and recorded motions in past New Zealand and global earthquakes.

Variations in uniform hazard spectra and disaggregated scenarios during earthquake sequences

Seismic hazard varies greatly during an earthquake sequence. Understanding this variation can be useful to end-users, such as emergency managers, as it would enable them to make more informed decisions about potential risk reduction measures. This article presents examples of how two commonly-used products of probabilistic seismic hazard assessments: uniform hazard spectra and disaggregated earthquake scenarios, vary during two severe seismic sequences in western Greece. These calculations are made using a recent time-dependent seismic hazard model based on a Bayesian ETAS approach. The examples show that time-dependent uniform hazard spectra for short return periods (1 and 10 years) are significantly higher than standard time-independent spectra but that uniform hazard spectra for the commonly-used return periods of 475 and 2475 years are similar to those from time-independent assessments. The time-dependent spectra generally converge within a couple of days to the time-independent spectra. The examples also show that the dominant earthquake scenarios evidenced by the disaggregation for the time-dependent assessment can show significant differences from the time-independent scenarios. This is particularly true when the earthquake sequence is distant from the location of interest as the aftershocks contribute greatly to the overall hazard. To show these changes more clearly this article introduces a new graphical representation of the disaggregated results: contour maps showing the magnitude or distance of the dominant earthquake scenario with axes of the structural period and response spectral acceleration.

Time-Dependent Seismic Hazard Assessment Based on the Annual Consultation: A Case from the China Seismic Experimental Site (CSES)

Time-Dependent Seismic Hazard Assessment Based on the Annual Consultation: A Case from the China Seismic Experimental Site (CSES)

Probabilistic long-term resilience of bridges under seismic and deterioration processes

Accurate long-term risk and resilience assessments of bridges are of paramount importance to aid rational decision making under seismic hazards. Both earthquakes and structural deterioration exhibit time-varying features. It has been found that the occurrence of large earthquakes is dependent on time, due to energy accumulation, whereas the widely adopted homogeneous Poisson process assumes a time-independent hazard occurrence. Bridges can deteriorate over time due to environmental exposure, resulting in increased seismic vulnerability. The time-varying characteristics associated with earthquakes and deterioration, which have compound effects on structures, should thus be incorporated in long-term seismic risk and resilience assessments. An approach for assessing the long-term resilience of bridges incorporating the time-varying characteristics of earthquakes and deterioration is presented. The Brownian passage time model, capturing energy accumulation and release, is used to model the time-varying characteristics of earthquakes. Bridge seismic vulnerability is computed in a time-varying manner considering deterioration. Subsequently, long-term bridge resilience loss is computed by considering earthquakes and deterioration over the entire service life of the bridge. The proposed approach is illustrated on a highway bridge subjected to time-dependent seismic hazard and structural deterioration.

Bayesian Parameter Estimation for Space and Time Interacting Earthquake Rupture Model Using Historical and Physics-Based Simulated Earthquake Catalogs

ABSTRACTThis article introduces a framework to supplement short historical catalogs with synthetic catalogs and determine large earthquakes’ recurrence. For this assessment, we developed a parameter estimation technique for a probabilistic earthquake occurrence model that captures time and space interactions between large mainshocks. The technique is based on a two-step Bayesian update that uses a synthetic catalog from physics-based simulations for initial parameter estimation and then the historical catalog for further calibration, fully characterizing parameter uncertainty. The article also provides a formulation to combine multiple synthetic catalogs according to their likelihood of representing empirical earthquake stress drops and Global Positioning System-inferred interseismic coupling. We applied this technique to analyze large-magnitude earthquakes’ recurrence along 650 km of the subduction fault’s interface located offshore Lima, Peru. We built nine 2000 yr long synthetic catalogs using quasi-dynamic earthquake cycle simulations based on the rate-and-state friction law to supplement the 450 yr long historical catalog. When the synthetic catalogs are combined with the historical catalog without propagating their uncertainty, we found average relative reductions larger than 90% in the recurrence parameters’ uncertainty. When we propagated the physics-based simulations’ uncertainty to the posterior, the reductions in uncertainty decreased to 60%–70%. In two Bayesian assessments, we then show that using synthetic catalogs results in higher parameter uncertainty reductions than using only the historical catalog (69% vs. 60% and 83% vs. 80%), demonstrating that synthetic catalogs can be effectively combined with historical data, especially in tectonic regions with short historical catalogs. Finally, we show the implications of these results for time-dependent seismic hazard.

Time-Dependent Seismic Hazard Analysis for Induced Seismicity: The Case of St Gallen (Switzerland), Geothermal Field

Reliable seismic hazard analyses are crucial to mitigate seismic risk. When dealing with induced seismicity the standard Probabilistic Seismic Hazard Analysis (PSHA) has to be modified because of the peculiar characteristics of the induced events. In particular, the relative shallow depths, small magnitude, a correlation with field operations, and eventually non-Poisson recurrence time. In addition to the well-known problem of estimating the maximum expected magnitude, it is important to take into account how the industrial field operations affect the temporal and spatial distribution of the earthquakes. In fact, during specific stages of the project the seismicity may be hard to be modelled as a Poisson process—as usually done in the standard PSHA—and can cluster near the well or migrate toward hazardous known or—even worse—not known faults. Here we present a technique in which we modify the standard PSHA to compute time-dependent seismic hazard. The technique allows using non-Poisson models (BPT, Weibull, gamma and ETAS) whose parameters are fitted using the seismicity record during distinct stages of the field operations. As a test case, the procedure has been implemented by using data recorded at St. Gallen deep geothermal field, Switzerland, during fluid injection. The results suggest that seismic hazard analyses, using appropriate recurrence model, ground motion predictive equations, and maximum magnitude allow the expected ground-motion to be reliably predicted in the study area. The predictions can support site managers to decide how to proceed with the project avoiding adverse consequences.

Influence of time-dependent seismic hazard on structural design

Recent works on seismic hazard have introduced the concept of time-dependent seismic hazard and different models have been proposed to predict the inter-arrival time between consecutive events. Currently, the reliability assessment of structures and relevant design rules proposed by the codes are based on the Poisson recursive model, for which the frequency of the occurrence of seismic events does not change over time. This paper presents results on the impact of Time-Dependent Seismic Hazard on structural design, by evaluating the strength required by the structure (seismic capacity) for different time intervals elapsing from the last event. “Seismic capacity” is understood here as the capacity required to provide a fixed reliability level, measured by the failure rate. Two different seismic scenarios have been investigated and results concerning different site-to-source distance, capacity dispersion of the structure and different recurrence properties of the time-dependent source have been discussed. Finally, the impact of recursive properties of time-dependent model is analysed and discussed. The results obtained from the analyses highlight a significant influence of time-dependent hazard properties on the structural capacity required to attain a target reliability, and give evidence to the different roles played by the parameters considered in the analysis. Within the set of the considered case studies, the ratios between seismic capacities evaluated by the time-dependent and non-time-dependent model span the range [0,1.32] in the first scenario, where inter-arrival time varies from 0 to two times the mean return period. The second scenario involves multiple sources and observed ratios were in the range [0.84,1.23], extreme values are relevant to inter-arrival times equal to 139 y and 371 y, respectively.

Tests of Remote Dynamic Aftershock Triggering by Small Mainshocks Using Taiwan’s Earthquake Catalog

Abstract To understand earthquake interaction and forecast time-dependent seismic hazard, it is essential to determine which static or dynamic stress change due to a mainshock plays a major role in triggering its aftershocks and subsequent mainshocks. Using small mainshocks (2≤M<3) and their aftershocks, Felzer and Brodsky (2006) argued that mainshock induced dynamic stress change is responsible for earthquake triggering in a form of power-law decay within 50 km. Richards-Dinger et al. (2010), however, studied the foreshock decay and claimed that mainshock had no effect at distances outside its static stress triggering range, which required an alternative explanation. We tested these hypotheses using Taiwan’s earthquake catalog by taking advantage of its lack of large events and the absence of active volcano and associated significant seismic swarm. In examining earthquakes occurring in 1994–2010, following Felzer and Brodsky’s method, we found a linear aftershock density with a power-law decay of −1.12±0.38 that is very similar to the one seen in Felzer and Brodsky (2006). None of the mainshock–aftershock pairs were associated with an M 7 rupture event or M 6 event. We further demonstrated that the density decay in a short time period is more likely a randomized behavior than mainshock–aftershock triggering. These pairs were located mostly in high geothermal gradient areas, which are probably triggered by a small-scale aseismic process.

Time-dependent seismic hazard and risk due to wastewater injection in Oklahoma

In the past decade, Oklahoma has experienced unprecedented seismicity rates, following an increase in the volumes of wastewater that are being disposed underground. In this article, we perform a probabilistic assessment of the time-dependent seismic hazard in Oklahoma and incorporate these results into an integrated seismic risk model to assess the evolution of the statewide economic losses, including a conservative forecast through 2030. Our risk model employs an injection-driven earthquake rate model, a region-specific ground motion model, a recent Vs30 map, HAZUS exposure data and updated vulnerability curves for both structural and nonstructural elements, and contents. The calculations are performed using a stochastic Monte Carlo–based approach implemented in the OpenQuake engine. The resulting seismic hazard maps illustrate the incompatibility of the regional seismic provisions with the current seismicity. In 2015, in particular, the induced seismic hazard in several places in Oklahoma was higher than along the San Andreas fault. During the peak of seismicity in 2015, the seismic risk was 275 times higher than the background level, with the vast majority of losses originating from damages to nonstructural elements and contents. Our direct economic loss estimates are in reasonable agreement with the paid insurance claims, but show significant sensitivity to the ground motion model selection. The proposed risk model, with possible regular updates on the seismicity rate forecast, can help stakeholders define acceptable production levels.

Spatio-temporal associations between dike intrusions and fault ruptures in the Tongariro Volcanic Center, New Zealand

Crustal extension of the southern portion of the Taupo Rift in the Central North Island of New Zealand is mostly accommodated by normal faulting and rare dike intrusions. To better understand how extension is accommodated and how volcanoes and faults interact, we provide a new integration of the tectonic and volcanic history of this young section of the Taupo Rift from geological evidence. Fault acceleration and deceleration apparently coincide with episodes of voluminous volcanic eruptions during the last 100 ka. Using geological data, we detect three modes of volcano-fault interactions active during different periods: (1) increased volcanism (eruptive volume) coupled with increased fault slip-rate (e.g., 26–11 cal kyr BP); (2) increased volcanism, but decreased adjacent fault activity (e.g., 11–10 cal kyr BP Pahoka-Mangamate “unzipping” period); and (3) decreased volcanism (low rates and volumes), but increased fault slip-rate (e.g., 45–25 cal kyr BP). The availability of melt production at depth is a first-order factor controlling the geodynamic processes of coeval fault slip-rate and magma volume variations within this rift. We hypothesize that progressive shallowing of magma drives transition of mode (1) to (2); i.e., maintaining high volcanic rates but decreasing fault slip. Second-order interactions, such as stress-transfer, is modelled by simple Coulomb stress transfer scenarios to other faults and volcanoes surrounding rift elements. Our results strongly suggest that fluctuations in magma input through time strongly influence both eruption frequency and seismic cycles in volcanic rifts. Time-dependent seismic hazard models must consider the influence of magmatic processes in fault parameters (e.g. temporal slip-rate variations) in continental rifting environments.

Spatial distribution of earthquake potential along the Himalayan arc

To determine the spatial distribution of earthquake potential along the active Himalayan arc, we utilize GPS measurements and earthquake data. We derive horizontal velocity field and 2-D strain rates from a new set of 41 regional GPS stations along with 446 published velocities. We convert these strain rate tensors to geodetic moment rate build-up within 24 contiguous segments and compare to the seismic moment rate release derived from a reassessed earthquake catalog of 900 years. The geodetic to seismic moment rate ratio, an indicator of stored strain energy, varies from below unity to more than 50 in different segments. The estimated geodetic moment rate ranges from 1.7 × 1018 Nm/yr to 10.2 × 1018 Nm/yr, whereas the seismic moment rate ranges from 3.7 × 1016 Nm/yr to 5.1 × 1019 Nm/yr. This variation between the geodetic and seismic moment rate corresponds to a moment deficit rate of ~1.15×1017 Nm/yr to 7.97 × 1018 Nm/yr along various segments of the study region. The above moment deficit rate provides an equivalent earthquake potential of magnitude 5.7 − 8.2 in different segments. Specifically, the higher earthquake potential (Mw≥8.0) corresponds to the segments in the central seismic gap and the northeast part of Himalaya, whereas the lower earthquake potential (Mw<7.0) corresponds to the segments encompassing the rupture areas of recent large events. The present findings not only provide input constraints on the contemporary crustal deformation but also contributes to the time-dependent seismic hazard analysis along the Himalaya.

Probabilistic Space- and Time-Interaction Modeling of Mainshock Earthquake Rupture Occurrence

ABSTRACTThis article presents a probabilistic formulation for modeling earthquake rupture processes of mainshocks. A correlated multivariate Bernoulli distribution is used to model rupture occurrence. The model captures time interaction through the use of Brownian passage-time distributions to assess rupture interarrival in multiple sections of the fault, and it also considers spatial interaction through the use of spatial correlograms. The correlograms represents the effect of rupture nucleation and propagation. This model is proposed as an attractive alternative to existing probabilistic models because it (1) incorporates time and space interactions of mainshocks, (2) preserves the marginal distributions of interarrival times after including spatial rupture interactions, that is, model consistency, and (3) has an implicit physical interpretation aligned with rupture behavior observations. The proposed model is applied to assess the occurrence of large interface earthquakes in the subduction fault along the coast of Lima, Peru. The model matches well both the annual magnitude exceedance rates and the average seismic moment release in the tectonic region. The Akaike information criterion (AIC) test confirms that our model performs statistically better than models that do not capture earthquake space interactions. AIC also shows that the spherical correlogram outperforms the exponential correlogram at reproducing earthquake data. Finally, time-dependent seismic hazard in the region is calculated, and the results demonstrate that by accounting for recent earthquake occurrences, the inclusion of time-dependent effects can reduce the 30 yr seismic hazard by a factor of 4.

Evaluation of The Seismic Hazard in The Marmara Region (Turkey) Based on Updated Databases

The increase in the wealth of information on the seismotectonic structure of the Marmara region after two devastating earthquakes (M7.6 Izmit and M7.2 Duzce events) in the year 1999 opened the way for the reassessment of the probabilistic seismic hazard in the light of new datasets. In this connection, the most recent findings and outputs of different national and international projects concerning seismicity and fault characterization in terms of geometric and kinematic properties are exploited in the present study to build an updated seismic hazard model. A revised fault segmentation model, alternative earthquake rupture models under a Poisson and renewal assumptions, as well as recently derived global and regional ground motion prediction equations (GMPEs) are put together in the present model to assess the seismic hazard in the region. Probabilistic seismic hazard assessment (PSHA) is conducted based on characteristic earthquake modelling for the fault segments capable of producing large earthquakes and smoothed seismicity modelling for the background smaller magnitude earthquake activity. The time-independent and time-dependent seismic hazard results in terms of spatial distributions of three ground-shaking intensity measures (peak ground acceleration, PGA, and 0.2 s and 1.0 s spectral accelerations (SA) on rock having 10% and 2% probabilities of exceedance in 50 years) as well as the corresponding hazard curves for selected cities are shown and compared with previous studies.

Stress change before and after the 2011 M9 Tohoku-oki earthquake

Megathrust systems hold important clues for our understanding of long- and short-term plate boundary dynamics, and the 2011 M9 Tohoku-oki earthquake provides a data-rich case in point. Here, we show that the F-net moment tensor catalog indicates systematic changes in crustal stress in the years leading up to the M9, due to the co-seismic effect, and for the last few years due to viscous relaxation. We explore the match between imaged stress change and the perturbations that are expected from 3-D, mechanical models of the visco-elastic relaxation and afterslip effects of the M9. While these models were constructed based on geodetic and structural seismology constraints alone, they match many characteristics of the seismicity-inferred stress change. This provides additional confidence in the modeling approach, and new clues for our understanding of plate boundary dynamics for the Japan trench. The success of deterministic approaches for exploring crustal stress change also implies that joint inversions using stress from focal mechanisms and geodetic constraints may be feasible. Such future efforts should provide key insights into time-dependent seismic hazard including earthquake triggering scenarios.

Re-estimate of Major Earthquake Activity in Surrounding Areas after the MS 6.6 Jinghe Earthquake in Xinjiang, 2017

According to theory, earthquakes may produce disturbances in surrounding areas and affect the major earthquake occurrence rate of surrounding faults. The MS 6.6 Jinghe Earthquake on 9th August, 2017 occurred in the Tienshan Seismic Belt where there is much tectonic activity and many strong earthquakes occur. The impact of this earthquake on major earthquake activity of surrounding areas is worth studying. This paper attempts to combine two models: the Brownian passage-time (BPT) model, which describes the quasi-periodic recurrence of major earthquakes, and the Coulomb Failure Stress model, which describes rock failure on faults. The amount of change in the rate of major earthquake occurrence caused by a nearby earthquake was calculated, and changes in major earthquake activity in the surrounding areas after the Jinghe Earthquake were re-estimated. There are few differences in major earthquake occurrence rate change by stress disturbances calculated with the BPT model or the Coulomb Failure Stress model. Calculation results are consistent with actual earthquake cases. The 2017 Jinghe Earthquake increased major earthquake activity on the Boluokenu Fault and Yili Basin North Fault, and the expected major earthquake recurrence times of the two faults were advanced by 11 years and 59 years, respectively. Conclusions of this paper provide a reference for time-dependent seismic hazard assessments in related areas.

A Bimodal Hybrid Model for Time-Dependent Probabilistic Seismic Hazard Analysis

The evaluation of evidence provided by geological studies and historical catalogs indicates that in some seismic regions and faults, multiple large earthquakes occur in cluster. Then, the occurrences of large earthquakes confront with quiescence and only the small-to-moderate earthquakes take place. Clustering of large earthquakes is the most distinguishable departure from the assumption of constant hazard of random occurrence of earthquakes in conventional seismic hazard analysis. In the present study, a time-dependent recurrence model is proposed to consider a series of large earthquakes that occurs in clusters. The model is flexible enough to better reflect the quasi-periodic behavior of large earthquakes with long-term clustering, which can be used in time-dependent probabilistic seismic hazard analysis with engineering purposes. In this model, the time-dependent hazard results are estimated by a hazard function which comprises three parts. A decreasing hazard of last large earthquake cluster and an increasing hazard of the next large earthquake cluster, along with a constant hazard of random occurrence of small-to-moderate earthquakes. In the final part of the paper, the time-dependent seismic hazard of the New Madrid Seismic Zone at different time intervals has been calculated for illustrative purpose.

Time-dependent seismic hazard analysis for the Greater Tehran and surrounding areas

This study presents a time-dependent approach for seismic hazard in Tehran and surrounding areas. Hazard is evaluated by combining background seismic activity, and larger earthquakes may emanate from fault segments. Using available historical and paleoseismological data or empirical relation, the recurrence time and maximum magnitude of characteristic earthquakes for the major faults have been explored. The Brownian passage time (BPT) distribution has been used to calculate equivalent fictitious seismicity rate for major faults in the region. To include ground motion uncertainty, a logic tree and five ground motion prediction equations have been selected based on their applicability in the region. Finally, hazard maps have been presented.