liminfoSeismic Reference
Free reference guide: Seismic Reference
About Seismic Reference
The Seismic Engineering Reference is a specialized quick-reference tool for earthquake engineering professionals, covering seismic wave propagation (P-wave, S-wave, surface waves), magnitude scales (Richter ML, moment magnitude Mw, surface wave Ms, body wave mb), and intensity measures (MMI, JMA, PGA/PGV/PGD). Each entry includes the governing equations, typical parameter values, and practical calculation examples.
This reference provides detailed coverage of seismic design codes including KDS 41 (Korean Building Code) provisions for importance classification, site classification (S1-S5 based on Vs30), design response spectrum construction, equivalent lateral force procedure, response modification factors (R), and allowable story drift limits. It also covers response spectrum analysis methods including SRSS and CQC modal combination techniques.
The ground engineering section addresses liquefaction assessment using the Seed & Idriss simplified procedure with SPT-based CRR calculation, site response analysis (1D equivalent linear SHAKE method), Vs30 measurement techniques (MASW, downhole, crosshole), site natural period estimation, and post-liquefaction deformation including lateral spreading and settlement. All formulas include the relevant correction factors and worked examples.
Key Features
- Complete P-wave, S-wave, and surface wave propagation equations with velocity formulas for crust, mantle, and core
- Magnitude scale comparisons (ML, Mw, Ms, mb) with saturation ranges and the Gutenberg-Richter energy-frequency relation
- KDS 41 seismic design provisions including site classification, design spectrum, base shear, and R-factor tables
- Response spectrum construction with characteristic periods T0, Ts, TL and damping correction factors
- SPT-based liquefaction assessment with CSR, CRR, magnitude scaling factor, and safety factor calculations
- GMPE (Ground Motion Prediction Equation) formulas including NGA-West2 and Korean peninsula-specific models
- Nonlinear time history analysis requirements: ground motion selection, spectrum matching, and integration methods
- Searchable and categorized into seismic waves, intensity, design codes, response spectrum, and geotechnical topics
Frequently Asked Questions
What seismic wave types are covered in this reference?
This reference covers P-waves (compressional, longitudinal), S-waves (shear, transverse), Love waves, and Rayleigh waves. Each entry includes the propagation velocity formula, typical velocities in different Earth layers, particle motion characteristics, and their significance for structural damage assessment.
How is moment magnitude (Mw) calculated?
Moment magnitude is calculated as Mw = (2/3) * log10(M0) - 10.7, where M0 is the seismic moment equal to the product of shear modulus, fault rupture area, and average slip (M0 = mu * A * D). Unlike Richter magnitude (ML), Mw does not saturate for large earthquakes and is the current international standard.
What KDS 41 design code information is included?
The reference covers KDS 41 seismic importance grades (Special through Grade 3 with importance factors), site classification S1-S5 based on Vs30, design spectral acceleration coefficients (SDS, SD1), equivalent lateral force base shear calculation, response modification factors for various structural systems, and allowable story drift ratios.
How do I use the liquefaction assessment formulas?
Follow the Seed & Idriss simplified procedure: calculate the Cyclic Stress Ratio (CSR) from peak ground acceleration and site stresses, determine the Cyclic Resistance Ratio (CRR) from corrected SPT blow count (N1)60, apply the magnitude scaling factor (MSF), and compute the factor of safety. FS >= 1.5 indicates safety against liquefaction.
What is the design response spectrum and how is it constructed?
The KDS 41 design response spectrum has four regions: a linear ramp from 0.4*SDS to SDS (T < T0), constant acceleration SDS (T0 to Ts), velocity-controlled SD1/T (Ts to TL), and displacement-controlled SD1*TL/T^2 (T > TL). The characteristic periods T0 and Ts are derived from the SDS and SD1 coefficients.
What are the SRSS and CQC modal combination methods?
SRSS (Square Root of Sum of Squares) combines modal responses as R = sqrt(Sum(Ri^2)) and is appropriate when modal periods differ by more than 10%. CQC (Complete Quadratic Combination) accounts for modal correlation through cross-terms and is recommended when closely-spaced modes exist. For directional combination, the 100%-30%-30% rule or SRSS is used.
What ground motion prediction equations are covered?
The reference includes the general GMPE functional form, the Boore & Atkinson (2008) NGA model for active shallow crust, Korean peninsula-specific attenuation relationships, and key parameters like Vs30, Joyner-Boore distance (Rjb), and rupture distance (Rrup). The NGA-West2 (2014) model suite is also referenced.
Is this reference suitable for practicing structural engineers?
Yes. The reference is designed as a practical quick-lookup for engineers performing seismic analysis and design. It includes the specific equations, R-factor tables, drift limits, and period formulas needed for code-based seismic design, along with geotechnical assessment methods for liquefaction and site response.