Seismic Mitigation Framework for Non-engineered Masonry Buildings in Developing Countries: Application to Malawi in the East African Rift

Novelli, Viviana; Kloukinas, Panos; Ngoma, Ignasio; Kafodya, Innocent; Macdonald, John H G; Goda, Katsuichiro

doi:10.1007/978-981-13-7446-3_8

Cited by 11 publications

(9 citation statements)

References 38 publications

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“…CC BY 4.0 License. and the proliferation of seismically vulnerable building stock (Delvaux et al, 2017;Giordano et al, 2021;Goda et al, 2016Goda et al, , 2021Hodge et al, 2015;Ngoma et al, 2019;Novelli et al, 2019). The geospatial, kinematic, and earthquake source data in the MSSD are freely available, and we suggest that the database will be an important resource for seismic hazard planning in the region.…”

Section: Introductionmentioning

confidence: 90%

Geologic and geodetic constraints on the seismic hazard of Malawi’s active faults: The Malawi Seismogenic Source Database (MSSD)

Williams

Wedmore

Fagereng

et al. 2021

Preprint

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Abstract. Active fault data are commonly used in seismic hazard assessments, but there are challenges in deriving the slip rate, geometry, and frequency of earthquakes along active faults. Herein, we present the open-access geospatial Malawi Seismogenic Source Database (MSSD), which describes the seismogenic properties of faults that have formed during East African rifting in Malawi. We first use empirical observations to geometrically classify active faults into section, fault, and multi-fault seismogenic sources. For sources in the North Basin of Lake Malawi, slip rates can be derived from the vertical offset of a seismic reflector that is estimated to be 75 ka based on dated core. Elsewhere, slip rates are constrained from advancing a ‘systems-based’ approach that partitions geodetically-derived rift extension rates in Malawi between seismogenic sources using a priori constraints on regional strain distribution in magma-poor continental rifts. Slip rates are then combined with source geometry and empirical scaling relationships to estimate earthquake magnitudes and recurrence intervals, and their uncertainty is described from the variability of outcomes from a logic tree used in these calculations. We find that for sources in the Lake Malawi’s North Basin, where slip rates can be derived from both the geodetic data and the offset seismic reflector, the slip rate estimates are within error of each other, although those from the offset reflector are higher. Sources in the MSSD are 5–200 km long, which implies that large magnitude (MW 7–8) earthquakes may occur in Malawi. Low slip rates (0.05–2 mm/yr), however, mean that the frequency of such events will be low (recurrence intervals ~103–104 years). The MSSD represents an important resource for investigating Malawi’s increasing seismic risks and provides a framework for incorporating active fault data into seismic hazard assessment in other tectonically active regions.

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Section: Introductionmentioning

confidence: 90%

Geologic and geodetic constraints on the seismic hazard of Malawi’s active faults: The Malawi Seismogenic Source Database (MSSD)

Williams

Wedmore

Fagereng

et al. 2021

Preprint

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“…CC BY 4.0 License. increased exposure to seismic hazard (World Bank, 2019;Goda et al, 2016;Hodge et al, 2015;Kloukinas et al, 2019;Ngoma et al, 2019;Novelli et al, 2019). Notably, previous PSHA in the EARS has typically been conducted using the ~65 year long instrumental record of seismicity alone (Ayele, 2017;Goitom et al, 2017;Midzi et al, 1999;Poggi et al, 2017).…”

Section: ;mentioning

confidence: 99%

A systems-based approach to parameterise seismic hazard in regions with little historical or instrumental seismicity: The South Malawi Active Fault Database

Williams¹,

Mdala²,

Fagereng³

et al. 2020

Preprint

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Abstract. Seismic hazard is frequently characterised using instrumental seismic records. However, in regions where the instrumental record is short relative to earthquake repeat times, extrapolating it to estimate seismic hazard can misrepresent the probable location, magnitude, and frequency of future large earthquakes. Although paleoseismology can address this challenge, this approach requires certain geomorphic settings and carries large inherent uncertainties. Here, we outline how fault slip rates and recurrence intervals can be estimated through an approach that combines fault geometry, earthquake-scaling relationships, geodetically derived regional strain rates, and geological constraints of regional strain distribution. We then apply this approach to the southern Malawi Rift where, although no on-fault slip rate measurements exist, there are theoretical and observational constraints on how strain is distributed between border and intrabasinal faults. This has led to the development of the South Malawi Active Fault Database (SMAFD), the first database of its kind in the East African Rift System (EARS) and designed so that the outputs can be easily incorporated into Probabilistic Seismic Hazard Analysis. We estimate earthquake magnitudes of MW 5.4–7.2 for individual fault sections in the SMAFD, and MW 6.0–7.8 for whole fault ruptures. These potentially high magnitudes for continental normal faults reflect southern Malawi's 11–140 km long faults and thick (30–35 km) seismogenic crust. However, low slip rates (intermediate estimates 0.05–0.8 mm/yr) imply long recurrence intervals between events: 102–105 years for border faults and 103–106 years for intrabasinal faults. Sensitivity analysis indicates that the large range of these estimates can be reduced most significantly from an improved understanding of the rate and partitioning of rift-extension in southern Malawi, earthquake scaling relationships, and earthquake rupture scenarios. Hence these are critical areas for future research. The SMAFD provides a framework for using geological and geodetic information to characterize seismic hazard in low strain rate settings with few on-fault slip rate measurements, and could be adapted for use elsewhere in the EARS or globally.

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“…According to the collected data described above, inspected buildings, as illustrated in Table 1, are classified in three typologies: A, B, and C (shown in Figure 3) introduced in the World Housing Encyclopedia by the authors [9,13] Typology A is representative for 20% of the inspected buildings, characterized by low seismic vulnerability (Figure 3 (a)). These buildings were made of mud mortar combined with fired bricks of poor fabric quality (see Figure 2(b3)) and unfired bricks from poor to high fabric quality (see Figure 2(a1), (a2), and (a3)).…”

Section: Buildign Classificationmentioning

confidence: 99%

“…During the first preliminary investigation carried out in Malawi by the authors to identify the prevalent building features and understand local construction practice, information was gathered from the Malawi Housing and Population Census [6] and World Housing Encyclopedia [7], and the Malawian Safer Housing Construction Guidelines [8]. As discussed in [9], collected data underlined high inconsistencies between datasets, highlighted by different criteria adopted to identify building typologies and distributions and non-compliance with design standards and guidelines.…”

Section: Introductionmentioning

confidence: 99%

Seismic Vulnerability Assessment of Non-Engineered Masonry Buildings in Malawi

Novelli¹,

Ngoma²,

Kloukinas³

et al. 2019

Proceedings of the 7th International Conference on Computational Methods in Structural Dynamics and Earthquake Engineering (COM

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Malawi is located within the southern branch of the active East African Rift System, where earthquakes of Mw 7.0 (or greater) can occur along major faults. In Malawi, the majority of dwellings in both formal and informal settlements are non-engineered unreinforced masonry constructions, built by local artisans with little input from engineers. These constructions are highly vulnerable to seismic events due to poor materials and lack of construction detailing. This study develops analytical vulnerability functions that enable the assessment of seismic capacity of typical buildings in Malawi. Since the seismic vulnerability greatly depends on building characteristics, geometrical and structural data are collected by conducting semirapid surveys of 300 houses located in urban and rural areas of Central and Southern regions of Malawi. Mechanical properties of the local materials are also obtained from an experimental campaign. In this work, a mechanical method FaMIVE (Failure Mechanism Identification and Vulnerability Evaluation) is adopted and the effects of both in-plane and out-ofplane behaviour of the masonry structures are taken into consideration to derive capacity curves for seismic vulnerability assessment. Special attention is given to 1) the Malawian building typologies as described in the Word Housing Encyclopedia and 2) failure mode classes for the Malawian constructions as calculated by FaMIVE. Hence, the derived vulnerability functions can serve as a benchmark for typical buildings in Malawi. The results and conclusions are also relevant for other East African countries, where similar construction techniques are adopted.

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Seismic Mitigation Framework for Non-engineered Masonry Buildings in Developing Countries: Application to Malawi in the East African Rift

Cited by 11 publications

References 38 publications

Geologic and geodetic constraints on the seismic hazard of Malawi’s active faults: The Malawi Seismogenic Source Database (MSSD)

Geologic and geodetic constraints on the seismic hazard of Malawi’s active faults: The Malawi Seismogenic Source Database (MSSD)

A systems-based approach to parameterise seismic hazard in regions with little historical or instrumental seismicity: The South Malawi Active Fault Database

Seismic Vulnerability Assessment of Non-Engineered Masonry Buildings in Malawi

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