Kinematic source example - 1994 Northridge earthquake
We use a model of the 1994 Northridge earthquake to illustrate how to set up kinematic models in SeisSol.
This Mw6.7 earthquake occurred in the San Fernando Valley region of Los Angeles, California, USA on January 17. The estimated duration of this typical reverse-slip earthquake ranges between 10 and 20s. The ruptured fault strikes N122\(^\circ\)E and dips at 40\(^\circ\).
The structural model is built with Gmsh. It features a planar fault of 20 km \(\times\) 25 km dipping 40 \(^\circ\), within a half-space region of 100 km \(\times\) 100 km \(\times\) 60 km
Kinematic rupture Source
Kinematic models in the standard rupture format can be used directly in SeisSol, after converting them to nrf with the rconv tool (see next and Multiple point-sources for more details), with the following lines in the parameter.par file:
&SourceType Type = 42 FileName=’northridge.nrf’ /
A description of the standard rupture format can be found at https://strike.scec.org/scecpedia/Standard_Rupture_Format. Please note that some variables describing the kinematic model are given in non SI units.
The fault of the Northridge model is divided into 20 point-sources along strike times 25 point-sources along dip. This can be seen in the SRF file header, whose format is the following:
version (1.0) PLANE 1 ELON ELAT NSTK NDIP LEN WID STK DIP DTOP SHYP DHYP POINTS NP
ELON top center longitude ELAT top center latitude NSTK number of point sources (subfaults) along strike NDIP number of point sources (subfaults) down-dip LEN segment length (km) WID segment width (km) STK segment strike DIP segment dip DTOP depth to top of fault segment (km) SHYP along strike location (from top center) of hypocenter for this segment (km) DHYP down-dip location (from top edge) of hypocenter for this segment (km) NP Number of points in fault plane
Each point source (subfault) is described in the file in a data block, with the following format:
LON LAT DEP STK DIP AREA TINIT DT RAKE SLIP1 NT1 SLIP2 NT2 SLIP3 NT3 SR1 SR1 SR1 . . . SR1[NT1] SR2 SR2 SR2 . . . SR2[NT3] SR3 SR3 SR3 . . . SR3[NT3] ...
LON: longitude of subfault center LAT: latitude of subfault center DEP: depth of subfault center (km) STK: strike DIP: dip AREA: area of subfault (cm^2) TINIT: initiation time when rupture reaches subfault center (sec) DT: time step in slip velocity function (sec) RAKE: direction of u1 axis (rake direction) SLIP1: total slip in u1 direction (cm) NT1: number of time points in slip rate function for u1 direction SLIP2: total slip in u2 direction (cm) NT2: number of time points in slip rate function for u2 direction SLIP3: total slip in u3 (surface normal) direction (cm) NT3: number of time points in slip rate function for u3 direction SR1,…,SR1[NT1] slip rate at each time step for u1 direction (cm/sec) SR2,…,SR2[NT2] slip rate at each time step for u2 direction (cm/sec) SR3,…,SR3[NT3] slip rate at each time step for u3 direction (cm/sec)
Project geographic coordinates
The geographic coordinates of the source model are projected to Cartesian coordinates with the pre-processing tool rconv.
rconv -i northridge.srf -o northridge.nrf -m "+proj=tmerc +datum=WGS84 +k=0.9996 +lon_0=-118.5150 +lat_0=34.3440" -x visualization.xdmf
The fault is ruptured over 7s, leading to a MW6.7 earthquake. A snapshot of the vertical ground-surface velocity at 7s after rupture onset in shown below.