LukeWedmore/malawi_seismogenic_source_model: Malawi Seismogenic Source Model v1.2

  • Jack N. Williams (University of Otago) (Creator)
  • Luke N. J. Wedmore (Creator)
  • Åke Fagereng (Creator)
  • Max Werner (Creator)
  • Juliet J Biggs (Creator)
  • Hassan Mdala (Creator)
  • Folarin Kolawole (Creator)
  • Donna J Shillington (Creator)
  • Zuze Dulanya (Creator)
  • Felix Mphepo (Creator)
  • Patrick R. N Chindandali (Creator)
  • Lachlan J M Wright (Creator)
  • Christopher A Scholz (Creator)

Dataset

Description

The Malawi Seismogenic Source Model (MSSM) is a geospatial database that documents the geometry, slip rate and seismogenic properties (ie earthquake magnitude and frequency) of active faults in Malawi. Each geospatial feature represents a potential earthquake rupture of 'source' and is classified based on its geometry into one of three types:

sectionfaultmulti-fault

Source types are mutually exclusice, and so if incorporated into a PSHA, they should be assigned relative weightings.

The MSSM is the first seismogenic source database in central and northern Malawi, and represents an update of the South Malawi Seismogenic Source Database (SMSSD; Williams et al., 2021a) because it incorporates new active fault traces (Kolawole et al., 2021; Williams et al., 2021b; 2022 - MAFD), new geodetic data (Wedmore et al., 2021) and a statistical treatment of uncertainty, within a logic tree approach.

The seismogenic sources in this model are adapted from the faults in the Malawi Active Fault Database (Williams et al., 2021b; 2022).

Prior to publication please cite this database using the following two references:

Williams, J. N., Wedmore, L. N .J., Fagereng, Å., Werner, M. J., Biggs, J., Mdala, H., Kolawole, F., Shillington, D. J., Dulanya, Z., Mphepo, F., Chindandali, P., Wright, L. J. M.., Scholz, C. A. Geological and geodetic constraints on the seismic hazard of Malawi's active faults: the Malawi Seismogenic Source Model (MSSM). <em>Manuscript submitted to Natural Hazards and Earth System Sciences</em>

Williams, Jack N., Wedmore, Luke N. J., Fagereng, Åke, Werner, Maximilian J., Biggs, Juliet, Mdala, Hassan, Kolawole, Folarin, Shillington, Donna J., Dulanya, Zuze, Mphepo, Felix, Chindandali, Patrick R. N., Wright, Lachlan J. M., &amp; Scholz, Christopher A. (2021). Malawi Seismogenic Source Model [Data set]. Zenodo. https://doi.org/10.5281/zenodo.5599616

Database Design and File Formats

The MSSM is a geospatial database that consists of two separate components:

A 3D geometrical model of fault seismogenic sources in MalawiThe mapped trace of each source in a GIS vector format, with associated source attributes (Data Table).

Each fault is associated with a source in the 3D geometrical model that is listed in a comma-separated-values (csv) file. The sections, faults and multi-faults that make up the individual seismogenic sources are described in separate geospatial files that describe the map-view geometry and metadata that control each sources earthquake magnitude and frequency for seismic hazard purposes.

The sections, faults and multi-faults in this database are provided in a variety of GIS vector file formats. GeoJSON is the version of record, and any changes should be made in this version before they are converted to other file formats using the script in the repository that uses the GDAL tool ogr2ogr (the script is adapted from https://github.com/cossatot/central_am_carib_faults/blob/master/convert.sh - we thank Richard Styron for making this publicly available). The other versions available are ESRI ShapeFile, KML, GMT, and GeoPackage.

 

List and brief description of the fault geometry, slip rate estimates and earthquake source attributes in the GIS vector format files that make up the MSSM.AttribugeTypeDescriptionNotesMSSM_IDintegerUnique numerical reference ID for each seismic sourceID 00-300 is section rupture
ID 300-500 is fault rupture
ID 600-700 is a multi-fault rupturenamestring Assigned based on previous mapping or local geographic feature.

For sections and faults, the name of the fault (flt_name) and larger multi-fault (mflt_name) system they are hosted on are given respectively.basinstringBasin that source is located within.Used in slip rate calculationsclassstringintrarift or border fault length (L<sub>s</sub>)real numberstraight-line distance in km between fault tips; sum of L<sub>sec</sub> for segmented faults; sum of L<sub>fault</sub> for multi-faultsmeasured in km to 1 decimal place. Must be greater than 5 km (except for linking sections).areaintegerCalculated from L<sub>s</sub> multiplied by Eq. 1 or based on fault truncation.measured in km<sup>2</sup>strikeintegerAzimuth of straigth line between the fault tips.
azimuth is &lt;180°
Used as input for slip rate estimates in Eq. 2
dip_lowerintegerlower range of dip valueWhen no previous measurements of dip are available, a nominal value of 45° is used.dip_intintegerIntermediate dip valueIn the MSSM geometrical model, only the intermediate measurements is considered. When no previous measurements of are available, a nominal value of 53° is assigned.

No dip is assigned for multi-fault sources, as different participating faults may have different dips.dip_upperintegerUpper range of dip valueWhen no previous measurements of dip are availabe, a nominal value of 65° is used.dip_dirstringDip direction: compass quadrant that the fault dips in. slip_typestringSource kinematics (e.g. normal, thrust etc).All sources in the MSSM are assumed to be normal faults.slip_ratereal numberMean value from repeating Eq. 2 in Monte Carlo simulations (see manuscript for details).In mm yr<sup>-1</sup>. All sources in the MSSM are assumed to be normal so is equivalent to dip-slip rate.

Reported to two significant figures.s_rate_errreal numberSlip rate error: 1σ error from Monte Carlo slip rate simlations. mag_lowerreal numberLower magnitude estimate.

Calculated from Leonard (2010) scaling relationship (Eq. 4) for L<sub>s</sub> or A<sub>s</sub>, and using lower estimates of C<sub>1</sub> and C<sub>2</sub> constants in Leonard (2010).Reported to one decimal place.mag_medreal numberMean magnitude estimate.

Calculated from Leonard (2010) scaling relationship (Eq. 4) for L<sub>s</sub> or A<sub>s</sub>, and using mean estimates of C<sub>1</sub> and C<sub>2</sub> constants in Leonard (2010).Reported to one decimal place.mag_upperreal numberUpper magnitude estimate.

Calculated from Leonard (2010) scaling relationship (Eq. 4) for L<sub>s</sub> or A<sub>s</sub>, and using upper estimates of C<sub>1</sub> and C<sub>2</sub> constants in Leonard (2010).Reported to one decimal place.ri_lowerreal numberLower recurrence interval estimate.

Calculated as 1σ below the mean of the Monte Carlo simulations (assuming a log normal distribution).Reported to two significant figures.ri_medreal numberMean recurrence interval.

Mean value from log of recurrence interval Monte Carlo simulations.Reported to two significant figures.ri_upperreal numberUpper recurrence interval estimate.

Calculated as 1σ above the mean of the Monte Carlo simulations (assuming a log normal distribution).Reported to two significant figures.MAFD_idlistList of integers of ID of equivalent structures in the Malawi Active Fault DatabaseMulti-fault sources have multiple ID's.

 

Version Control

This version is intended to be "Live" and as such we encourage edits of the GeoJSON file and the submission of pull requests. Please contact Jack Williams [email protected] Luke Wedmore [email protected] or Hassan Mdala [email protected] for information, other requests or if you find any errors within the database.

It is the intention that future versions of this database will include fault slip rates that have been determined from direct geological methods (e.g. offset stratigraphy that has been dated) rather than the systems based approach that is currently used.

 

References

Kolawole, F., Firkins, M. C., Al Wahaibi, T. S., Atekwana, E. A., &amp; Soreghan, M. J. (2021a). Rift Interaction Zones and the Stages of Rift Linkage in Active Segmented Continental Rift Systems. <em>Basin Research</em>. https://doi.org/10.1111/bre.12592

Leonard, M. (2010). Earthquake fault scaling: Self-consistent relating of rupture length, width, average displacement, and moment release. <em>Bulletin of the Seismological Society of America</em>, 100(5A), 1971-1988. https://doi.org/10.1785/0120090189

Wedmore, L. N. J., Biggs, J., Floyd, M., Fagereng, Å., Mdala, H., Chindandali, P. R. N., et al. (2021). Geodetic constraints on cratonic microplates and broad strain during rifting of thick Southern Africa lithosphere. <em>Geophysical Research Letters</em>. 48(17), e2021GL093785. https://doi.org/10.1029/2021GL093785

Williams, J. N., Mdala, H., Fagereng, Å., Wedmore, L. N. J., Biggs, J., Dulany, Z., et al. (2021). 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. Solid Earth, 12(1), 187–217. https://doi.org/10.5194/se-12-187-2021

V1.1 Updates

Updated seismic source files and model parameters. Changes are:


Adding lower and upper dip estimates for sources (following a reviewer comment). This should be equivalent to Table 1 in the revised manuscript.

Cleaning up the GIS files. In the old file there were some duplicate GIS features that are now removed

Changing the name and acronyms from Malawi Seismogenic Source Database (MSSD) to Malawi Seismogenic Sources Model (MSSM).


 


Included a basic Matlab script to plot the MSSM geometrical polygons


V1.2 Updates

Updated fault source geometry .csv file due to compiling error.
Date made available30 Sept 2022
PublisherZenodo

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