Abstract
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.
Highlights
Earthquake ruptures tend to occur on pre-existing faults (Brace and Byerlee, 1966; Jackson, 2001; Scholz, 2002; Sibson, 1989)
Be appropriate for low-strain intraplate settings where geodetic data cannot resolve deformation rates (Calais et al, 2016), By applying this approach to southern Malawi, we have developed the South Malawi Seismogenic Source Database (SMSSD), which is a complementary database to the South Malawi Active Fault Database (SMAFD) but where the attributes are (1) targeted towards its inclusion in probabilistic seismic hazard analysis (PSHA) and (2) derived from modelling
We describe a new systems-based approach that combines geologic and geodetic data to estimate fault slip rates and earthquake recurrence intervals in regions with little historical or paleoseismic earthquake data
Summary
Earthquake ruptures tend to occur on pre-existing faults (Brace and Byerlee, 1966; Jackson, 2001; Scholz, 2002; Sibson, 1989). In some regions, the fault mapping in these databases has only been performed at a coarse scale, and the fault attributes (e.g. slip rates, earthquake recurrence intervals) that are required to use them as earthquake sources in PSHA have not been measured. Where the instrumental record is relatively short compared with fault recurrence intervals and where earthquakes may be especially damaging (England and Jackson, 2011) It would not, be appropriate for low-strain intraplate settings where geodetic data cannot resolve deformation rates (Calais et al, 2016), By applying this approach to southern Malawi, we have developed the South Malawi Seismogenic Source Database (SMSSD), which is a complementary database to the SMAFD but where the attributes (e.g. fault segmentation, earthquake recurrence intervals) are (1) targeted towards its inclusion in PSHA and (2) derived from modelling (and are mutable).
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