Afifa Imtiaz

Last Name

Imtiaz

First Name

Afifa

ORCID

0000-0001-6687-8690

Organisational unit

02818 - Schweiz. Erdbebendienst (SED) / Swiss Seismological Service (SED)

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Publications 1 - 10 of 12

Extending ERM-CH23 to shallow induced seismicity in Switzerland
Grigoratos, Iason; Bergamo, Paolo; Cauzzi, Carlo Virgilio; et al. (2025)
The risks from induced seismicity remain a persistent and complex issue that needs to be managed. Appropriate modeling of these risks is essential in order to facilitate both the permitting process of certain energy-production projects and the acquisition of insurance against potential losses. For Switzerland, the most relevant causal factors of induced seismicity are likely hydraulic stimulations for Enhanced Geothermal Systems and fluid disposal for storage. The earthquakes that these activities might trigger are expected to be quite shallow, of mostly small to moderate magnitude. Their nucleation mechanism might also differ, compared to tectonic events. Thus, their source characteristics and the attenuation of their ground motion might be partly incompatible with the modeling assumptions adopted by the national Earthquake Hazard Model of Switzerland (SUIhaz2015; Wiemer et al., 2016; Papadopoulos et al., 2024a). This report investigated these issues, as well as, the possibility that the fragility models of the Earthquake Risk Model of Switzerland (ERM-CH23; Wiemer et al., 2023) might warrant modifications for similar reasons.. The results of these investigations highlighted the need to adjust some aspects of the risk model to render it suitable for (shallow) induced seismicity in Switzerland. In the end, new recommendations were made regarding the minimum and maximum magnitude, two new intensity measures were added to the vulnerability models, while major changes were made to the ground shaking branching level. The latter is now magnitude-dependent, only includes spectral acceleration models and was tilted towards lower stress-parameter values. A ready to use version of the updated risk model, called Induced Earthquake Risk Model of Switzerland (IERM-CH25), is now available. Finally, risk calculations, including sensitivity analyses, were conducted for certain scenario earthquakes at selected sites.
Erneuerung des Starkbebennetzwerks in der Schweiz (2009‐2023) - Abschlussbericht
Fäh, Donat; Duvernay, Blaise; Michel, Clotaire; et al. (2024)
Mit seinem Beschluss vom 18. Februar 2009 hat der Bundesrat den Antrag für die Erneuerung des Starkbebennetzes der Schweiz (Phase 1) gutgeheissen und deren Realisierung in Auftrag gegeben. Das Projekt umfasst in dieser ersten Phase (2009‐2013) die Installation und Inbetriebnahme von 30 modernen Erdbebenstationen. Diese sollen in erster Linie bestehende Lücken in der nationalen Überwachung schliessen. Dabei wurden alte Stationen teilweise ersetzt, aber auch neue Standorte realisiert. Im Rahmen des Projektes wurden neue Standards für die Installation von Starkbebenstationen definiert. Aufgrund der erfolgreichen ersten Phase hat der Bundesrat mit seinem Beschluss vom 30. Januar 2013 der Realisierung der zweiten Phase der Erneuerung des Starkbebenmessnetzes (2013‐2023) zugestimmt. In dieser zweiten Phase werden 70 Starkbebenmessstationen gebaut, davon vier Bohrlochinstallationen. Abbildung 1 gibt einen Überblick über die 100 Starkbebenstationen, die in den Phasen 1 und 2 installiert wurden. Beide Projektphasen wurden von einer Steuerungsgruppe unter der Leitung des Bundesamts für Umwelt (BAFU) begleitet. Für alle installierten Stationen wurde eine Standortcharakterisierung durchgeführt. Dabei kamen Ein‐Stations‐Methoden der seismischen Bodenunruhe, passive Arraymessungen und aktive seismische Messungen zum Einsatz. An Standorten mit besonderen Bodeneigenschaften, die bei Erdbeben zu nichtlinearem Materialverhalten oder Bodenverflüssigung neigen, wurden CPT‐ Messungen durchgeführt. Die Standortcharakterisierung wurde für jeden Standort in einem Bericht zusammengefasst. Die Messdaten und Auswertungen wurden in einer Datenbank gespeichert. Eine Beschreibung der Standorte und die Berichte zur Standortcharakterisierung sowie die Erdbebenaufzeichnungen der Starkbebenstationen sind auf den Webseiten des Schweizerischen Erdbebendienstes zugänglich.
Shear-wave velocity profiles and their relationship with empirical amplification functions
Panzera, Francesco; Chieppa, Dario; Bergamo, Paolo; et al. (2022)
Proceedings of the Third European Conference on Earthquake Engineering and Seismology – 3ECEES
From a one-dimensional shear-wave velocity profile, the quarter-wavelength approach allows computing travel-time averaged parameters such as velocity and impedance contrast. The advantage of such a procedure is the possibility of relating the averaging depth to a specific wavelength, thus making the result frequency-dependent. In this study we converted a set of velocity profiles into its quarter-wavelength representation. Results are then correlated with empirical amplification functions. For this purpose, we use a database of empirical amplification functions and shear wave profiles of the Swiss seismic network. We demonstrate that quarter-wavelength parameters can be used as proxy for seismic site characterization of rock and soft sediment sites and to derive site-dependent amplification functions.
A scenario-based earthquake loss assessment for Basel
Imtiaz, Afifa; Papadopoulos, Athanasios N.; Bergamo, Paolo; et al. (2023)
Abstract Volume 21st Swiss Geoscience Meeting
Characterization and modeling of ground motion at depth in soft sedimentary rocks: Application to the Swiss Molasse Basin
Halló, Miroslav; Imtiaz, Afifa; Koroni, Maria; et al. (2023)
Soil Dynamics and Earthquake Engineering
The level of earthquake motion observed on the ground surface differs from the shaking at locations buried at a depth. Characterization of the underground shaking is important for the local seismic hazard assessment at depth which is an insufficiently investigated topic so far. Advancements in the prediction of the ground motion at depth are especially important for the design of deep geological disposals of nuclear waste, buildings with deep foundations, or studies focused on soil-structure interactions. In this paper, we analyze site-specific transfer functions that relate ground motions on the surface to that at a depth at sites located within soft sedimentary rocks of the Swiss Molasse Basin. We first evaluate empirical surface-to-borehole amplification functions at six borehole sites, compare them with predictions by a theoretical model, and characterize the high-frequency surface-to-borehole amplification. Next, we perform full-waveform prediction of ground motion at depth from surface recordings of seven significant regional earthquakes with ML > 4. The comparison of predicted and observed acceleration waveforms shows a high level of similarity in a broad frequency range and well-predicted values of PGA, PGV, and response spectra. Finally, we model a scenario earthquake for 9975 years return period at a test site, and we predict associated broadband waveforms at depth. By the latter, we demonstrate that our method to predict ground motions at depth can be used as a basis for the site-specific seismic hazard of deep geological disposals of nuclear waste.
Application of canonical correlation for assessing site amplification in Basel, Switzerland
Imtiaz, Afifa; Panzera, Francesco; Fäh, Donat (2022)
Proceedings of the Third European Conference on Earthquake Engineering and Seismology – 3ECEES
This study presents an ongoing work on developing a high-resolution site-amplification model at an urban scale for the canton of Basel-City in Switzerland. A database of Empirical Amplification Functions (EAFs) computed from stations of the national seismic networks of Switzerland along with shear-wave velocity (Vs) profiles and Horizontal-to-Vertical Noise Ratios (HVNRs) of ambient vibrations at those sites are used to derive canonical correlations between the HVNRs and EAFs. They are applied to predict the expected EAFs at sites of 21 seismic stations in Basel in order to verify the accuracy of the method. After validation, the method is to be applied to predict EAFs for a dense network of sites where geophysical measurements are available from ambient vibration and Vs profiles from the three-dimensional geophysical model. Results of the validation phase indicate that the canonical correlation method can be promising in predicting amplification where no empirical functions are available.
Understanding building damage through the lens of the Swiss post-seismic reconnaissance mission of 2023 Al Haouz, Morocco, earthquake
Imtiaz, Afifa; Saloustros, Savvas; Beqiraj, Meriton; et al. (2025)
Scientific Reports
A team of scientists and engineers from Swiss institutions participated in a post-seismic reconnaissance mission in Morocco following the magnitude 6.8 earthquake of September 8, 2023. We visited different heavily affected towns and villages, located from 10 to 70 km epicentral distance, in the High Atlas Mountain and Marrakech. In this work, we report our observations from inspecting building damage in affected areas. We discuss the prevalent building typologies observed, their construction mechanisms, and the resulting structural and non-structural damage patterns. We also examine the potential site-related effects based on a literature review of the seismological and geological settings of the area. The earthquake's severe impact was due to its shallow depth and underlying geological complexities, including active faulting and diverse rock formations. The lack of earthquake-resistant construction practices significantly exacerbated the damage. Modern structures in Marrakech were largely unaffected while ancient ones in the Medina of Marrakech suffered partial damage. In rural High Atlas areas, buildings exhibited significant damage due to lack of seismic design as well as poor-quality materials. Our observations prompt us to believe that conducting site-specific hazard studies along with implementing earthquake-proofing measures involving local communities can foster resilience to future seismic events in this area.
Effects of Surface and Underground Topography on GroundMotion: an Overview of Some Recent European Collaborative Results
Bard, P.Y.; Cultrera, G.; Theodoulidis, N.; et al. (2015)
Seismological Research Letters
Estimation of site-specific amplification function from quarter-wavelength velocity profile and its application to obtain local amplification maps
Panzera, Francesco; Bergamo, Paolo; Imtiaz, Afifa; et al. (2024)
Engineering Geology
Quarter-wavelength (QWL) velocity refers to the S-wave velocity at a depth equal to one-fourth of the wavelength of the seismic waves. It provides valuable information about the characteristics of the subsurface material properties affecting seismic waves propagation. The Swiss Seismological Service (SED) network, with over 200 stations across different lithologies, offers a rich dataset to implement correlation between site properties and site amplification factors. The current study is based on a subset of 113 selected SED seismic stations for which shear-wave velocity (Vs) profiles from geophysical measurements are available. We first meticulously analyzed and adjusted them to accurately determine the bedrock depth of the sites they are located on. Using empirical spectral modelling (ESM), we computed amplification functions from recorded earthquakes, referenced to the Swiss standard rock profile with a VS30 of 1100 m/s. Then we performed a bivariate analysis between empirical amplification functions, QWL velocity and QWL velocity contrast. The resulting coefficients are used to predict elastic amplification at frequencies between 0.5 and 10 Hz, with predictions generally being within 20–28% of observed values. We also developed an empirical equation relating VS30 (time-averaged Vs to 30 m depth) and κ0 (high-frequency attenuation parameter), to incorporate the anelastic term in the amplification. Applying our method to a 3D geophysical model of Visp, a high seismic hazard zone in Switzerland, we found it effective in predicting 1D site amplification, but noted caution in areas susceptible of 2D/3D resonance effects. A calibration function based on observed vs. predicted amplification and the frequencies of estimation normalized by the expected 2D resonance frequency improved predictions for Visp. Our study demonstrates that QWL velocity profiles offer a straightforward approach for characterizing site effects, which can be used in seismic hazard assessment to evaluate the potential amplification of ground motions.
An integrated 3D geological-seismological model at urban scale in Basel, Switzerland
Imtiaz, Afifa; Panzera, Francesco; Halló, Miroslav; et al. (2021)
6th IASPEI / IAEE International Symposium: Effects of Surface Geology on Seismic Motion - ESG6 Extended Abstracts
This work presents a prototype of seismic site response study at urban scale, performed in the context of developing an earthquake risk model for the canton of Basel-City in Switzerland. Different studies undertaken over the last two decades in this area concluded that unconsolidated sediments were responsible for inducing resonance and large amplification of seismic waves over frequencies pertinent to engineering interest. They also highlighted the necessity of better characterizing complex geological domains (the Upper Rhine Graben and the Tabular Jura) and tectonic setting (the master fault system of the Graben) of the area. Therefore, we present a conceptual framework and an initial attempt in this study to develop a 3D integrated geological-seismological model of Basel, which will explicitly account for the complex geological settings at the surface and at depths. This model will be used to further simulate 3D amplification effects and risk scenarios for Basel city.

Publications 1 - 10 of 12

Afifa Imtiaz

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