Earthquake Shaking Research Articles

Comparing single-station 6C measurements and array measurements for seismic microzonation in Munich, Germany

SUMMARY The essential goal of seismic microzonation is the estimation of the shallow velocity structure in order to characterize the local earthquake shaking characteristics. This is of special importance in densely inhabited areas with unfavourable soil conditions. The common approach is the analysis of ambient noise array data using frequency–wavenumber (FK) or spatial autocorrelation (SPAC) techniques. However, the installation of arrays is difficult, especially within urban environments, making single-station approaches more desirable. In this study, we directly compare the recently developed approach of velocity estimation using single-station six-component (6C) measurements, combining three translational and three rotational motions, with the established methods of FK and SPAC analysis. We conduct measurements in Munich’s inner city using a geophone array and an iXblue blueSeis-3A rotational motion sensor together with a Nanometrics Trillium Compact Seismometer, respectively. From the array data, as well as from the 6C data, Love and Rayleigh dispersion curves are estimated and further inverted for 1-D P- and S-wave velocity profiles. We find that all methods give similar results, indicating the potential of the novel 6C approach. Furthermore, adding horizontal-to-vertical spectral ratios enables the inversion for structures at greater depth and increases the resolution of the velocity structure. In addition, we test different array geometries to evaluate the influence of the sensor configuration on the results. As a last step, we compare the estimated velocity models to lithologic profiles and find an overall positive correlation, which supports our inversion results.

Dynamic characteristics of built heritage using ambient noise recordings

The paper addresses the investigation of the dynamic characteristics of a case study, the Egyptian church of Abu serga. To this aim some in situ investigations have been conducted and related results are discussed. The paper presents interesting and innovative aspects, mainly related to the characteristics of the church investigated, covering a lack of knowledge in the scientific literature due to the typology of the church. The integrated geotechnical and geophysical investigation techniques assessed the level of seismic and other geo-environmental risks that Abu serga church suffers from. It suffers multiple Geo-environmental hazards. The main objectives of this pilot study are as follows: (1) Identifying the shear velocity Vs analysis profile of the subsoil and also the resonant frequency of soil and the historical building of Abu serga church using ambient noise recordings (microtremors) to assess the level of seismic and other geo-environmental hazards. (2) Understanding the damage to the historic building caused by the recent earthquakes. (3) Offering technical support and advice on intervention retrofitting for the historic damaged structure.In this study, ambient noise recordings have been processed through horizontal to vertical spectral ratios to examine the main frequencies and to examine whether the building has its main frequency close to that of the soil in order to identify potential resonance phenomena. Numerous ambient noise recordings were recorded on the soil, in the basement, and at each floor of the buildings.This study suggests moderate level of earthquake activity at Abu serga church and is in a good agreement with the fact that “Egypt is a part of the stable African Shield”, but the existence of old structures such as the Abu serga church may reduce the ability to resist any earthquake shaking.

Seismic vulnerability of jacket supported large offshore wind turbine considering multidirectional ground motions

Large numbers of offshore wind turbines in earthquake prone areas increase the scientific interest in analysing their seismic vulnerability. This study investigates the deformation and collapses susceptibility of a 10 MW jacket supported offshore wind turbine (OWT) considering different geometry of pile and jacket. A three-dimensional finite element model of the soil-pile-jacket-tower is developed in ABAQUS. A performance-based analysis is conducted to quantify the engineering demand parameters by choosing first mode spectral acceleration as the intensity measure for different pile length-to-diameter ratios and the base width of the jacket. The significance of considering higher modes and the vertical component of the earthquake motion on the dynamic response of offshore wind turbines is also discussed. Considerable amplification of acceleration is observed at the nacelle due to vertical excitation. In low to moderate earthquake shaking, jacket base width shows a marginal influence on the responses, while a significant impact is observed for strong earthquake shaking. Mudline rotation and acceleration response at the nacelle are the most critical parameters that govern the design under the serviceability limit state. Moreover, it is observed that initiation of the rocking mode of vibration for jacket-supported OWTs resting on a pile foundation is significantly less until its embedment length reduces considerably (3 to 5 m).

To Evaluate the Seismic Response of a Building Having Stiffness Irregularity and Plan Irregularity with Quintuple Friction Pendulum System

Abstract: Quintuple friction pendulum (QFPS) bearing is a new generation sliding isolation system having multiple spherical sliding surfaces. The friction isolation system with single sliding surface is designed for a specific level of ground shaking, which may prove ineffective in case of other hazard levels. The QFPS bearing on the other hand, exhibits adaptive behavior and imparts greater amount of flexibility to the designer for various levels of earthquake shaking. Here, the effectiveness of Quintuple Friction pendulum system is carried out to study the seismic demands of base-isolated building frames with stiffness irregularities and plan irregularities subjected to various earthquake ground motions i.e. Far field ground motion, near field ground motion with fling step and near field ground motion with forward directivity by comparing their estimates with the benchmark responses obtained by the Non-Linear Time History Analysis (NLTHA). SAP 2000 Software has been used for the same. The two soft storey buildings and two buildings with plan irregularity will be modelled and analyzed. The seismic demands namely, Inter story drift, peak storey acceleration, maximum base shear are considered for the study.The reduction in absolute acceleration is found more in case of PI as compared to SS for all the considered time histories. The reduction in Maximum Base-Shear is found more in case of Plan irregularity as compared to Stiffness Irregularity (Soft Story) in all the considered Time History. In isolated structure, the Inter-storey drift is found to be maximum in case of structure having soft storey as compared to plan irregularity 1 and 2. Keywords: Multi storied RC structures, Plan irregularities, Soft storey, Quintuple Friction Pendulum, Non linear Time History Method(NLTHM)

Adverse Impact of Earthquake Seismic Loading on Angular Offset Tunnels and Effects of Isolation Grout

This paper investigates the effects of seismic loads on tunnels in an attempt to provide better protection from earthquake shaking. Dynamic analysis of angular offset tunnels was performed, and the tunnels’ behavior under earthquake shaking and their response when using seismic isolation were analyzed in detail. The time history analysis was used to compute the stresses and deformation that develop in the tunnels during seismic events. Earthquake records with different frequency spectra were applied as seismic excitation to the twin tunnels. The excitation was applied normally to the tunnel axis, with peak ground accelerations of 0.10 g–0.30 g. The seismic event lasted 15 s, with a time step of 0.02 s utilized in the numerical analysis. Finite element modeling was employed to simulate the soil–tunnel interaction. Numerical models simulated twin tunnels passing through soft clay or stiff clay, with various earthquake records applied as seismic inputs. The effects of a silicon-based isolation material composed of silicon oil and fly-ash were compared with the use of traditional grout. The numerical model results show how seismic isolation affects the stresses and deformations that happen in tunnel bodies during earthquakes.

The enigmatic 1693 AD tsunami in the eastern Mediterranean Sea: new insights on the triggering mechanisms and propagation dynamics

The disastrous earthquake of 1693 AD caused over 60,000 causalities and the total destruction of several villages and towns in south-eastern Sicily. Immediately after the earthquake, a tsunami struck the Ionian coasts of Sicily and the Messina Strait and was probably recorded even in the Aeolian Islands and Malta. Over the last few decades, the event has been much debated regarding the location of the seismogenic source and the possible cause of the associated tsunami. The marine event has been related to both a submarine landslide and a coseismic displacement at the seafloor. To better define the most reliable sources and dynamics of the tsunami, we couple high-resolution marine seismic survey data with hydrodynamic modelling to simulate various scenarios of tsunami generation and propagation. Results from the simulations are compared with geomorphological evidence of past tsunami impacts, described in previous work along the coast of south-eastern Sicily, and within historical chronicles and reports. The most reliable scenario considers the 1693 event composed by two different tsunami waves: a first wave generated by the coseismic fault displacement at the seafloor and a second wave generated by a submarine landslide, triggered by the earthquake shaking. Tsunami modelling shows that a simultaneous movement between fault displacement and submarine mass movement could determine a destructive interference on the tsunami waves, resulting in a reduction in wave height. For this reason, the second tsunami wave probably occurred with a maximum delay of few minutes after the one generated by the earthquake and induced a greater flooding. The double-source model could explain the observation because in the course of other destructive earthquakes in south-eastern Sicily, such as that of 1169 AD, the associated tsunami caused less damages. This implies the need to better map, define and assess the hazard responsible for this type of tsunami events.

Behavioral responses to earthquake shaking: Video footage analysis of the 2016 Kaikōura earthquake in Wellington, Aotearoa New Zealand

Initiatives such as the ShakeOut earthquake drill (run nationally in Aotearoa New Zealand since 2012) are effective at teaching the protective actions “drop, cover, and hold” which can reduce the likelihood of injury during earthquakes. However, our understanding of human behavior during actual shaking is limited. Previous work has used retrospective self-reports to explore what actions people take during and immediately after an earthquake. While informative, such data is exposed to biases common in these types of methods. It is therefore important to complement the previous research with more objective data. This research builds on previously-developed methods of analyzing Closed Circuit Television (CCTV) footage to examine actions taken during the 2016 Kaikōura earthquake at Wellington International Airport, Aotearoa New Zealand. Only one of the 68 codable individuals was observed to undertake “drop, cover, and hold” as recommended in New Zealand, although a quarter took some kind of protective action (e.g. dropping or covering). The majority responded by standing, walking, looking around, or helping those near them. Because this earthquake had distinct P-wave and S-waves, we were able to examine changes in behavior caused by increases in shaking intensity. Among the 36 individuals who could be observed during the strong S-wave jolt, 27 changed their behavior; 11 changed from not protecting themselves to taking at least one protective action, and another 8 who were already undertaking at least one protective action took a further one or more steps to protect themselves. Among the 10 people observed to have an uncontrolled response to the sudden increase in shaking intensity, nine were taking no actions to protect themselves demonstrating the importance of taking protective actions before the arrival of strong shaking. This article presents key considerations for CCTV analysis and useful observations of behavior during earthquake shaking which can help to reduce injuries and fatalities.

In-field dynamic response of instrumented wine tanks subjected to aftershock earthquakes

An experimental investigation of the dynamic behaviour of anchored flat-based wine storage tanks in a winery located in Marlborough, New Zealand is presented herein. Six wine storage tanks with different dimensions, capacities, and anchorage systems were instrumented with accelerometers for approximately six weeks following the 2016 Kaikōura earthquake, providing an opportunity to conduct a parametric study of their dynamic response when subjected to 37 aftershock earthquakes. The largest accelerations measured in the horizontal (X and Y) and vertical (Z) axes directions at the top of the six tanks occurred in conjunction with a Mw5.48 aftershock earthquake, with analysis indicating that the peak acceleration at the tank top occurred along the horizontal (Y) axis with a value of 0.545 g.Analysis of accelerations recorded at the top of the six tanks revealed that for low-intensity earthquake shaking the largest accelerations were measured at the top of the 40kL tank. A comparison of the tank instrumentation data indicated that the 175kL tank with a shear bolt anchorage system performed better than the nominally identical 175kL tank with a necked tension anchorage system, with the maximum lateral accelerations attained in the horizontal X and Y axes directions for the tank with the necked tension anchorage system being on average 1.59 times and 1.39 times the acceleration attained for the tank with the shear bolt anchorage system. Analysis of the results for the highest intensity earthquake shaking (Mw5.48) also indicated that the two tanks with installed energy dissipation systems sustained less acceleration when compared to tanks with a traditional anchorage system. Also, good agreement was observed between the values of the impulsive period attained from the analysis of the tank instrumentation data and from finite element (FE) modal analysis.

Topographic Control on Ground Motions and Landslides From the 2015 Gorkha Earthquake

AbstractLandslides triggered by earthquake shaking pose a significant hazard in active mountain regions. Steep topography promotes gravitational instabilities and can amplify the seismic wavefield; however, the relationship between topographic amplification and landsliding is poorly understood. Here, we use numerical methods to investigate the link between low‐frequency ground shaking, topographic amplification, and the landslide distribution from the 2015 Gorkha, Nepal earthquake. Results show that the largest landslides initiated where the highest topographic amplification, highest elevations, and steepest slopes converged, typically in glacially‐sculpted terrain, with additional controls of rock strength and absolute ground motions. Additionally, the initiation of the largest and most fatal landslide was likely influenced by amplification throughout the rupture due the orientation of the ridge with respect to the propagating wavefield. These results indicate that topographic amplification is one of the key factors for understanding where large and potentially devastating landslides are likely to occur during future major earthquakes.

Modeling Seismic-Soil-Pile Interaction (SSPI) Problems for Large Pile Groups

This paper presents a critical review of the current challenges in analyzing large, realistic pile groups in soft clay soil under earthquake shaking. The review focuses on three main essentials of numerical analyses, namely soil behavior and constitutive model, pile and pile-soil interface modeling and computational framework.

Seismic performance of controlled outrigger rocking wall system with different energy dissipation devices

Controlled outrigger rocking wall (CORW) system is a novel earthquake resilient structural system that combines a reinforced concrete wall with an outrigger and a controlled rocking base. At the ends of the outrigger and the wall base, different dampers are used to dissipate earthquake energy. In this paper, a prototype 100 m, CORW building, is designed using the novel equivalent energy design procedure (EEDP). EEDP allows engineers to design the CORW to achieve different performance objectives at different levels of earthquake shaking intensities. The design of the CORW using dampers with different hysteretic behavior is presented in this paper. In addition, detailed numerical models for the CORW system were developed, and the seismic performance of the prototype CORW system with different dampers was systematically compared using nonlinear dynamic analyses. The result shows that the CORW can be efficiently designed using EEDP, and the desired performance of the CORW can be achieved using dampers with different hysteresis behavior. Hence, this paper demonstrates that CORW can be used as an efficient alternative seismic force resisting system for high-rise applications.

Design of a fuse link beam-to-column connection for earthquake resistant moment frames

This paper presents details of numerical investigations on exterior beam-column joint sub-assemblages with a novel fuse link beam-to-column connection. The connection is designed to protect the connected beams and columns of moment frame buildings during strong earthquake shaking by confining the inelasticity within the connection elements. The connection consists of two fuse links and one standard shear tab. Detailed numerical analyses are performed to study the behaviour of the connection including the level of plastic strain distribution around the connection region. First, the results of numerical analyses are validated using experimental results of full-scale experimental investigations on exterior beam-column joint sub-assemblages, which demonstrated the good performance and replaceability of the connection. Then, parametric studies are carried out to identify and investigate the effect of major parameters on the connection behaviour - the key parameters being the geometric parameters of fuse link and the beam depth. Finally, it is shown that the results of the numerical study are in good agreement with those of an analytical model that can be used for proportioning of the fuse link connection at the design stage. Also, the results of the analytical model can be used in global analysis of moment frames using the developed fuse link connection.

Bayesian networks for assessment of disruption to school systems under combined hazards

Exposure of school buildings to floods and earthquakes poses significant risk to the vulnerable population of students and their education process. In regions of high exposure, these hazards may often act concurrently, whereby yearly flood events weaken masonry school buildings, rendering them more vulnerable to frequent earthquake shaking. This recurring damage, combined with other functional losses, ultimately result in disruption to education delivery. The socio-economic condition of the users-community also plays a role in the extent of such disruption. A complex problem of this nature demands consideration of a large number of dimensions, to estimate the impact to the school system infrastructure in a locality. To handle the qualitative and quantitative nature of these variables, a Bayesian network (BN) model is proposed representing multiple schools in a locality as a system. Three dimensions are considered to contribute to the system disruption, namely, schools’ physical functionality loss, accessibility and use loss, and social vulnerability. The impact is quantified through the probability of the system being in various states of disruption. The BN also explores mitigating measures, such as the mobility of students between schools in the system. The general methodology is illustrated by a case-study of school buildings in Guwahati, India, whereby the majority of buildings is constructed in confined masonry with varying level of seismic performance. The physical effects of combined flood and seismic action on confined masonry buildings is assessed by nonlinear numerical modelling, and their probabilistic occurrence is expressed in terms of fragility functions corresponding to varying flood depth and peak ground acceleration.

Simplified solution for seismic earth pressures exerted on flexible walls

Seismic earth pressures acting on basement walls and retaining walls are most commonly computed using limit state methods, in which the effects of earthquake shaking are represented by a horizontal body force in an active soil wedge. Limit state methods provide a poor physical representation of the fundamental mechanisms that give rise to seismic earth pressures, which depend on relative wall–soil displacements. Such displacements are a consequence of soil–structure interaction, which, in the absence of a strong inertial component (e.g. from a connected structure), are mainly sensitive to the ratio of wavelength-to-wall height and relative wall-to-soil flexibility. We present a simplified single-frequency procedure for computing seismic earth pressures applied to flexible retaining structures by vertically propagating shear waves. The procedure accounts for the first-order wavelength and wall flexibility effects while simplifying a number of secondary effects in a manner that produces a slightly conservative outcome. Input parameters to the proposed solution are readily attainable for engineering design applications. For typical earth retention systems, earth pressures computed using the proposed procedure are lower than those computed using limit state solutions. Predictions from the proposed solution compare well with results of numerical simulations and centrifuge modeling from literature, whereas limit state procedures either do not provide a physically meaningful solution or produce strongly biased predictions (overprediction of experiments, underprediction of available simulations).

Effect of soil gradation on embankment response during liquefaction: A centrifuge testing program

This paper describes a centrifuge study undertaken to investigate how sand gradation affects the system-level performance of embankments subjected to strong shaking. Current analysis and design practices are primarily based on knowledge from case history records of liquefaction, with the majority of those from sites consisting of clean, poorly graded sands. The narrow range of gradation characteristics represented in the case history database poses a challenge during the analysis of embankment structures traditionally constructed with, or founded on, more broadly graded soils. The tests herein were designed to elucidate how embankments uniformly constructed with a well graded and poorly graded sand perform differently during earthquake shaking. A centrifuge experiment test program was developed and conducted using the 9-m-radius centrifuge at the UC Davis Center for Geotechnical Modeling. The experiment design consisted of two submerged 10-degree embankments positioned side-by-side in the same rigid model container, with one embankment constructed with poorly graded sand and the other with well graded sand. The embankments were dry pluviated to the same relative density, but the absolute densities of the sands were different. The embankments were identically instrumented with dense arrays of in-situ sensors beneath the level ground above the slope and in the mid-slope to measure the dynamic response during liquefaction. Results showed that embankments constructed at equal relative densities would both liquefy (i.e., ru reach 1.0), but deformations were less severe for the embankments constructed with the well graded sand. Greater resistance to the generation and faster dissipation of excess porewater pressures, coupled with stronger dilatancy of the well graded sand increased embankment stability, curtailing liquefaction-induced deformations.

Regional liquefaction-induced ground displacement predictions for Canada using 5th Generation NBCC Seismic Hazard Model

Significant regions of Canada are seismically active, and areas underlain by loose, saturated sediments in these regions are expected to experience liquefaction-induced lateral spread permanent ground displacements (PGDs) under earthquake shaking. The empirical predictive equations are commonly used for estimating the PGDs especially when detailed numerical analyses are not undertaken. The key input parameters for these equations comprise earthquake magnitude (M) and source distance (R), along with geotechnical and topographic parameters; however, there is ambiguity over choosing appropriate site-specific values of M and R. The current study predicts PGD probabilistic hazard curves that are applicable for locations in southwestern and southeastern regions of Canada using a probabilistic seismic hazard assessment (PSHA) framework. This was achieved by embedding two relevant empirical models for predicting lateral spread PGDs (replacing the ground motion prediction equations) within the 2015 National Building Code of Canada framework that is currently available in OpenQuake platform. Moreover, deaggregation analyses have been performed to understand the M and R contributions from different seismic sources on the predicted site-specific hazard. The developed PGD curves can be readily adopted for estimating site-specific lateral spread PGD demand as input to performance-based design of structures in seismically active areas of Canada.

Evacuation Behavior and Information Needs of Wellington, Aotearoa New Zealand Residents Following the 5 March 2021 Mw 7.3 East Cape Earthquake

Abstract At 2.27 a.m., on 5 March 2021, an Mw 7.3 earthquake occurred approximately 100 km off the East Cape of the North Island of Aotearoa New Zealand. This earthquake was felt across the entire country, including in the capital city of Wellington and the surrounding region. Previous work reports varied levels of tsunami evacuation behavior for natural warnings from earthquake shaking. To further explore this behavior, we surveyed residents of the Wellington region about their evacuation decisions following the 5 March East Cape earthquake, their motivations for evacuating or not evacuating, and their immediate information needs. Approximately one-third of those who felt the earthquake, and who were in a tsunami hazard zone, self-evacuated, similar to previous findings following a larger, closer earthquake in 2016. Reasons for evacuating immediately were evenly split over specific awareness of the National Emergency Management Agency’s “Long or strong, get gone” tsunami evacuation advice, general knowledge that earthquakes can trigger tsunami, and social influences. Among those who did not evacuate, common reasons included not receiving an official warning and not believing that the earthquake was strong enough to generate a tsunami. Most people sought information from GeoNet, an official provider of earthquake information, though civil defense and emergency management sources were less used than mainstream news and social media. Along with information about tsunami risk, people tended to seek or want general information about earthquake characteristics such as location and size. Overall, the findings suggest that current public education efforts to encourage people to recognize and act on natural warnings (i.e., earthquake shaking) rather than waiting for official advice should be continued, and that consideration should be given to encouraging the use of official information sources.

Geodetic and seismological analysis of the CROPOS ZAGR station kinematics during the Zagreb 2020 ML 5.5 earthquake

The CROPOS’s ZAGR stations, one of 33 stations of the Croatian permanent GNSS (Global Navigation Satellite System) network CROPOS (Croatian Positioning System), is located in Zagreb’s city centre. For the first time, motion of one of the CROPOS stations (the ZAGR station) during an earthquake shake (the Zagreb 2020 ML5.5) was analysed by the PPK (Post-Processed Kinematic) method using all available GNSS signals (GPS – Global Positioning System, GLONASS – GLObalnaya NAvigatsionnaya Sputnikovaya Sistem, Galileo, Bei-Dou) and seismologically interpreted. The ZAGR station is situated about 9 km to the south-southeast of the earthquake’s epicentre. The analysis showed that the station’s movements, i.e. combined surface and building motion, during the shake was far above the noise level and enabled the assessment of the station’s kinematics: movements in the range of approx. 13 cm in direction north–south (N–S) and approx. 6 cm in direction east–west (E–W). However, movements in the vertical direction were slightly above the noise level. Even though the ZAGR station kinematic behaviour was pronounced, no permanent displacement was identified. The seismological analysis showed that the ZAGR station recorded the onset of the SV-waves on the N–S component, surface waves on the N–S (predominantly Rayleigh waves) and E–W (mainly Love waves) components. The resolution of 1 s of the results of the PPK method have enabled a thorough analysis of the ZAGR station kinematics and pointed out the usefulness of the method in earthquake observations.

Centrifuge study of seismic response of soil-nailed walls supporting a footing on the ground surface

Seismic design of soil-nailed walls requires demonstrations of tolerable ranges of wall movements, especially when a surcharge load exists near the wall. In this study, the effect of surcharge location on seismically induced wall movements was investigated using four centrifuge tests. The axial tensile forces, developed along the soil nails during the seismic loadings, were also measured during the tests. At 50g centrifugal acceleration, model tests represented a 12 m high prototype wall reinforced with five rows of soil nails. To apply a surcharge stress of 30 kPa at the specified location relative to the wall for each model test, a rigid footing was placed on the soil surface. The model soil-nailed walls were subjected to three successive earthquake motions. Surprisingly, it was found that the model wall with the footing located behind the soil-nailed region experienced the largest seismic movements, even more than when the footing was directly behind the wall. Furthermore, the tests showed that the lower soil nails played a key role in the wall stability during earthquake shaking, acting as a pivot for the pre-collapse cases tested, whereas the upper soil nails needed to be sufficiently extended to contribute properly to the seismic stability of the wall.

From information to public preparedness in the Cascadia Subduction Zone: Examining risk communication outcomes in Metropolitan Portland, OR

A Cascadia Subduction Zone (CSZ) earthquake will cause widespread damage along the Pacific Northwest (PNW) coast of the United States. It is, therefore, crucial to understand how to reduce future impacts across this region and assess current levels of household preparedness. Here, we examine whether decades of risk and preparedness campaigns have established protective knowledge and promoted hazard adjustments for residents of the Portland, Oregon metropolitan (PDX) region, an area where risk and preparedness campaigns have been increasing over the last decade. We also explore how PDX preparedness levels compare to those in other PNW regions using analogous data from multiple surveys over a 20-year time interval and assess PDX respondent’s perceptions of risk information sources. We find that 63% of PDX residents do not intend to “Drop, Cover, and Hold On” (DCHO) when earthquake shaking starts and that, although residents are generally aware of earthquake hazards in the area, they are less aware of the specific risks for their homes. Furthermore, PDX residents’ preparedness levels seem to be comparable to those recently surveyed in Washington, but somewhat less than those surveyed two decades ago in California, though more comprehensive data are needed to verify these results. We also find that people rate risk information provided by emergency managers and their websites as more accurate, understandable, relevant, and new than other sources. Our results suggest that significant gaps remain in translating broad awareness of the CSZ earthquake into personal knowledge and preparedness. This work provides guidance to PDX emergency educators for more targeted messaging and provides methods to measure preparedness variables in other regions for future comparisons. By paying close attention to preparedness gaps, local officials can use their limited resources more effectively to develop strategies to inform their communities and improve preparedness before a major earthquake strikes.