Testing Fault Models in Intraplate Settings: A Potential for Challenging the Seismic Hazard Assessment Inputs and Hypothesis?

Vallage, Amaury; Bollinger, Laurent

doi:10.1007/s00024-019-02129-z

Cited by 11 publications

(9 citation statements)

References 38 publications

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“…Alternatively, the relatively thick (30-35 km) seismogenic crust in southern Malawi means that even moderate-large earthquakes (M W > 6) do not necessarily result in surface rupture, as illustrated by the M W 6.3 Salima earthquake (Gupta, 1992;Jackson and Blenkinsop, 1993). Finally, except for studies around Lake Malombe (Van Bocxlaer et al, 2012), there is no chronostratigraphic control for this section of the EARS to help differentiate between inactive and active faults (Dulanya, 2017;Wedmore et al, 2020a).…”

Section: Identifying Active and Inactive Faults In Southern Malawimentioning

confidence: 99%

A systems-based approach to parameterise seismic hazard in regions with little historical or instrumental seismicity: active fault and seismogenic source databases for southern Malawi

et al. 2021

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Abstract. Seismic hazard is commonly characterised using instrumental seismic records. However, these records are short relative to earthquake repeat times, and extrapolating 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 setting, is resource intensive, and can carry large inherent uncertainties. Here, we outline how fault slip rates and recurrence intervals can be estimated by combining fault geometry, earthquake-scaling relationships, geodetically derived regional strain rates, and geological constraints of regional strain distribution. We apply this approach to southern Malawi, near the southern end of the East African Rift, and where, although no on-fault slip rate measurements exist, there are constraints on strain partitioning between border and intra-basin faults. This has led to the development of the South Malawi Active Fault Database (SMAFD), a geographical database of 23 active fault traces, and the South Malawi Seismogenic Source Database (SMSSD), in which we apply our systems-based approach to estimate earthquake magnitudes and recurrence intervals for the faults compiled in the SMAFD. We estimate earthquake magnitudes of MW 5.4–7.2 for individual fault sections in the SMSSD and MW 5.6–7.8 for whole-fault ruptures. However, low fault 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 intra-basin faults. Sensitivity analysis indicates that the large range of these estimates can best be reduced with improved geodetic constraints in southern Malawi. The SMAFD and SMSSD provide a framework for using geological and geodetic information to characterise seismic hazard in regions with few on-fault slip rate measurements, and they could be adapted for use elsewhere in the East African Rift and globally.

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Section: Identifying Active and Inactive Faults In Southern Malawimentioning

confidence: 99%

A systems-based approach to parameterise seismic hazard in regions with little historical or instrumental seismicity: active fault and seismogenic source databases for southern Malawi

et al. 2021

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“…Many intraplate faults show evidence for strong temporal clustering of earthquakes and very low recurrence rates (10 to 100 kyr) (D. Clark et al, 2008, 2012, 2015; Cox et al, 2006; Crone et al, 1997, Craig et al, 2016; 2003; Gold et al, 2019; Stahl et al, 2016; Vallage & Bollinger, 2019). One intraplate faulting record that clearly demonstrates this behavior is from the Cadell Fault, in southeastern Australia.…”

Section: Understanding and Modeling The Temporal Distribution Of Fault Activitymentioning

confidence: 99%

“…Similarly, the aperiodicity and spatial and temporal clustering observed in the Otago region implies that a fault that is in an active state in this type of setting may pose a higher level of hazard than would be estimated from the long-term rate alone, although it is unclear why. Finally, the identification of intraplate faults with such long recurrence intervals requires the use of long paleoseismic records, sometimes much longer than can be obtained by instrumentally recorded seismicity (10 to 100 years) (Vallage & Bollinger, 2019), and these faults can be hard to detect or show little geologic or geomorphic evidence of past rupture. This in turn raises questions as to how informative the spatial distribution of recently observed seismicity is for forecasting future hazard, leading to deep epistemic uncertainty regarding how to characterize seismicity rates for PSHA (c) Probability density function and the cumulative distribution function for a Weibull probability model with the time axis normalized to the mean recurrence interval and various shape parameters.…”

Section: Implications For Pshamentioning

confidence: 99%

Seismic Hazard Analyses From Geologic and Geomorphic Data: Current and Future Challenges

et al. 2020

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The loss of life and economic consequences caused by several recent earthquakes demonstrate the importance of developing seismically safe building codes. The quantification of seismic hazard, which describes the likelihood of earthquake-induced ground shaking at a site for a specific time period, is a key component of a building code, as it helps ensure that structures are designed to withstand the ground shaking caused by a potential earthquake. Geologic or geomorphic data represent important inputs to the most common seismic hazard model (probabilistic seismic hazard analyses, or PSHAs), as they can characterize the magnitudes, locations, and types of earthquakes that occur over long intervals (thousands of years). However, several recent earthquakes and a growing body of work challenge many of our previous assumptions about the characteristics of active faults and their rupture behavior, and these complexities can be challenging to accurately represent in PSHA. Here, we discuss several of the outstanding challenges surrounding geologic and geomorphic data sets frequently used in PSHA. The topics we discuss include how to utilize paleoseismic records in fault slip rate estimates, understanding and modeling earthquake recurrence and fault complexity, the development and use of fault-scaling relationships, and characterizing enigmatic faults using topography. Making headway in these areas will likely require advancements in our understanding of the fundamental science behind processes such as fault triggering, complex rupture, earthquake clustering, and fault scaling. Progress in these topics will be important if we wish to accurately capture earthquake behavior in a variety of settings using PSHA in the future. Plain Language Summary Growing infrastructure and increasing population have caused significant loss of life due to recent large earthquakes, with the 2008 M w 7.9 Wenchuan and 2005 M w 7.6 Kashmir earthquakes each causing greater than 50,000 deaths. These earthquakes highlight the need for the development of building codes designed to withstand the strong ground shaking caused by earthquakes, as reinforced infrastructure is one of the most important factors for preventing fatalities due to ground shaking from earthquakes. Identifying the seismic hazard of a region, or the likelihood of ground shaking at a site due to potential earthquakes over time, is a key ingredient for informing a defensible building code. Here, we focus on current and future advances in how data from the fields of geology and geomorphology contribute to the most widely used type of seismic hazard model. These geologic data represent vital components to seismic hazard models, as they can provide information about the location and types of earthquakes that can occur over long, thousands of years, time periods, that cannot be obtained using other methods. We discuss some of the most pressing scientific issues about these data that are important for the development of seismic hazard models and defensible building codes.

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“…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). However, low EARS strain rates (regional extension rates ~1-6 mm/yr; Stamps et al, 2018) imply that this record is incomplete and may underestimate seismicity rates compared to those inferred from geodesy and paleoseismology (Ebinger et al, 2019;Hodge et al, 2015;Stein et al, 2012;Vallage and Bollinger, 2019). Hence, by providing more complete earthquake sources for PSHA, active fault databases in the EARS may play an important role in characterising its ever-increasing seismic risk (Goda et al, 2016;Hodge et al, 2015).…”

Section: ;mentioning

confidence: 99%

“…In addition, we also outline how the uncertainties and alternative hypotheses that are inherent to this approach can, in common with seismic hazard practice elsewhere, be explored with a logic tree approach (Fig. 6;Field et al, 2014;Vallage and Bollinger, 2019;Villamor et al, 2018).…”

Section: A Systems-based Approach To Estimating Earthquake Source Parmentioning

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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Testing Fault Models in Intraplate Settings: A Potential for Challenging the Seismic Hazard Assessment Inputs and Hypothesis?

Cited by 11 publications

References 38 publications

A systems-based approach to parameterise seismic hazard in regions with little historical or instrumental seismicity: active fault and seismogenic source databases for southern Malawi

A systems-based approach to parameterise seismic hazard in regions with little historical or instrumental seismicity: active fault and seismogenic source databases for southern Malawi

Seismic Hazard Analyses From Geologic and Geomorphic Data: Current and Future Challenges

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

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