Technical Studies

Earthquake Ground Motions with 2% Probability of Exceedence in 50 Years

Seattle

The table below provides detailed information on the records generated for Seattle having probabilities of exceedence of 2% in 50 years. These acceleration time histories have been derived from historical recordings or from physical simulations and have been altered so that their mean response spectrum matches the 1997 NEHRP design spectrum, modified from soil type of S_B-S_C to soil type S_D and having a hazard specified by the 1997 USGS maps.

There are 20 different horizontal components (10 2-component records). Each original historical ground motion pair has typically been altered in the following way:

The two horizontal components originally provided were resolved into fault-normal and fault-parallel orientations.
The records are adjusted in the frequency domain to have characteristics appropriate for NEHRP S_O soil sites.
The records are amplitude scaled so that the average of the two horizontal spectra match the target spectrum.
The individual components were rotated 45 degrees away from the fault-normal fault-parallel orientations

Additional details can be found from the main Ground Motions page. This page also provides a link to a draft report summarizing all of the SAC Phase 2 ground motion studies.

To see the acceleration time history of any of the ground motions listed in the table below, just click on the ground motion name.

Details of Seattle Ground Motions Having a
Probability of Exceedence of 2% in 50 Years
SAC Name	Record	Earthquake Magnitude	Distance (km)	Scale Factor	Number of Points	DT (sec)	Duration (sec)	PGA (cm/sec²)
SE21	1992 Mendocino	7.1	8.5	0.98	3000	0.02	59.98	741.13
SE22	1992 Mendocino	7.1	8.5	0.98	3000	0.02	59.98	476.22
SE23	1992 Erzincan	6.7	2	1.27	4156	0.005	20.775	593.60
SE24	1992 Erzincan	6.7	2	1.27	4156	0.005	20.775	529.06
SE25	1949 Olympia	6.5	56	4.35	4000	0.02	79.98	878.23
SE26	1949 Olympia	6.5	56	4.35	4000	0.02	79.98	805.68
SE27	1965 Seattle	7.1	80	10.04	4092	0.02	81.82	1722.40
SE28	1965 Seattle	7.1	80	10.04	4092	0.02	81.82	1364.70
SE29	1985 Valpariso	8	42	2.9	4000	0.025	99.975	1605.50
SE30	1985 Valpariso	8	42	2.9	4000	0.025	99.975	1543.50
SE31	1985 Valpariso	8	42	3.96	4000	0.025	99.975	1246.20
SE32	1985 Valpariso	8	42	3.96	4000	0.025	99.975	884.43
SE33	Deep Interplate (simulation)	7.9	65	3.84	4000	0.02	79.98	781.31
SE34	Deep Interplate (simulation)	7.9	65	3.84	4000	0.02	79.98	634.36
SE35	1978 Miyagi-oki	7.4	66	1.78	4000	0.02	79.98	595.07
SE36	1978 Miyagi-oki	7.4	66	1.78	4000	0.02	79.98	768.62
SE37	Shallow Interplate (simulation)	7.9	15	0.94	4000	0.02	79.98	552.52
SE38	Shallow Interplate (simulation)	7.9	15	0.94	4000	0.02	79.98	524.55
SE39	Shallow Interplate (simulation)	7.9	15	1.49	4000	0.02	79.98	567.18
SE40	Shallow Interplate (simulation)	7.9	15	1.49	4000	0.02	79.98	735.22

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