Abstract
Abstract. We generate synthetic catalogs of seismicity in northern California using a composite simulation. The basis of the simulation is the fault based "Virtual California" (VC) earthquake simulator. Back-slip velocities and mean recurrence intervals are specified on model strike-slip faults. A catalog of characteristic earthquakes is generated for a period of 100 000 yr. These earthquakes are predominantly in the range M = 6 to M = 8, but do not follow Gutenberg-Richter (GR) scaling at lower magnitudes. In order to model seismicity on unmapped faults we introduce background seismicity which occurs randomly in time with GR scaling and is spatially associated with the VC model faults. These earthquakes fill in the GR scaling down to M = 4 (the smallest earthquakes modeled). The rate of background seismicity is constrained by the observed rate of occurrence of M > 4 earthquakes in northern California. These earthquakes are then used to drive the BASS (branching aftershock sequence) model of aftershock occurrence. The BASS model is the self-similar limit of the ETAS (epidemic type aftershock sequence) model. Families of aftershocks are generated following each Virtual California and background main shock. In the simulations the rate of occurrence of aftershocks is essentially equal to the rate of occurrence of main shocks in the magnitude range 4 < M < 7. We generate frequency-magnitude and recurrence interval statistics both regionally and fault specific. We compare our modeled rates of seismicity and spatial variability with observations.
Highlights
Probabilistic seismic hazard analysis (PSHA) is of importance in assessing risk, allocating resources for risk mitigation, and establishing the basis for earthquake insurance premiums and establishing licensing criteria for nuclear power plants
We conclude that most main shocks in the magnitude range 4 < M < 7 occur on faults not included in the Virtual California (VC) simulation
In order to complete our catalog of main shocks in northern California we carry out a statistical simulation of background seismicity
Summary
Probabilistic seismic hazard analysis (PSHA) is of importance in assessing risk, allocating resources for risk mitigation, and establishing the basis for earthquake insurance premiums and establishing licensing criteria for nuclear power plants. In order to complete the specification of main shock seismicity we generate a set of background earthquakes that satisfy Gutenberg-Richter frequency-magnitude statistics, these earthquakes occur randomly in time and are spatially associated with the mapped faults We take both the fault based and the background earthquakes as parents which generate families of aftershocks. As a specific example we consider northern California and generate a synthetic 100 000 yr catalog of all earthquakes with M ≥ 4 and compare the results with observed seismicity. In this paper our objective is to model seismicity with M ≥ 4 in northern California and to compare the results with observations The basis of this model is a fault based simulation using VC which includes major mapped strike-slip faults in the region. We will obtain a 100 000 yr catalog of earthquakes and will examine the statistics of this seismicity
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