Stress Drop Calculator
Free Stress drop Calculator for geology & geophysics. Enter variables to compute results with formulas and detailed steps.
Formula
Stress Drop = (7/16) * M0 / r^3
For a circular fault, stress drop equals (7/16) times the seismic moment M0 divided by the cube of the fault radius r (Eshelby, 1957). The fault radius can be estimated from the corner frequency using the Brune (1970) model.
Worked Examples
Example 1: M6.0 Earthquake with 5 km Fault Radius
Problem: Calculate stress drop for M0 = 1.12e18 N*m and circular fault radius of 5 km.
Solution: Stress drop = (7/16) * M0 / r^3\n= (7/16) * 1.12e18 / (5000)^3\n= 0.4375 * 1.12e18 / 1.25e11\n= 3.92e6 Pa = 3.92 MPa = 39.2 bar
Result: Stress drop = 3.92 MPa (39.2 bar)
Example 2: Stress Drop from Corner Frequency
Problem: Estimate stress drop for a Mw 4.0 earthquake with corner frequency of 3.5 Hz.
Solution: M0 = 10^(1.5*4+9.1) = 1.26e15 N*m\nr = 2.34*3500/(2*pi*3.5) = 372.6 m\nStress drop = (7/16)*1.26e15/372.6^3 = 10.65 MPa
Result: Stress drop = 10.65 MPa, source radius = 373 m
Frequently Asked Questions
What is earthquake stress drop?
Stress drop is the difference between the stress on a fault before and after an earthquake. It represents the amount of shear stress released during fault slip, measured in units of pressure (Pa, MPa, or bars). For most tectonic earthquakes, stress drops range from about 0.1 to 100 MPa, with a typical value around 1-10 MPa. Stress drop is a key parameter controlling the strength of high-frequency ground motion and is important for seismic hazard assessment.
How does stress drop relate to earthquake damage?
Higher stress drop earthquakes produce relatively stronger high-frequency ground motion, which is more damaging to short-period structures such as one- to two-story buildings. Two earthquakes with the same magnitude but different stress drops will produce different shaking characteristics. A high stress drop event radiates more energy per unit fault area and generates stronger acceleration pulses. This is why stress drop is an important parameter in ground motion prediction equations used for seismic building code design.
What controls the stress drop of an earthquake?
Stress drop depends on fault roughness, rock strength, confining pressure, pore fluid pressure, and slip history. Interplate earthquakes (at plate boundaries) typically have lower stress drops of 1-5 MPa, while intraplate earthquakes (within tectonic plates) tend to have higher stress drops of 5-50 MPa. Deeper earthquakes generally have higher stress drops due to increased confining pressure. Some studies suggest that stress drop is approximately constant (self-similar) across magnitude ranges, but this remains debated in seismology.
Can I use Stress Drop Calculator on a mobile device?
Yes. All calculators on NovaCalculator are fully responsive and work on smartphones, tablets, and desktops. The layout adapts automatically to your screen size.
Can I use the results for professional or academic purposes?
You may use the results for reference and educational purposes. For professional reports, academic papers, or critical decisions, we recommend verifying outputs against peer-reviewed sources or consulting a qualified expert in the relevant field.
How accurate are the results from Stress Drop Calculator?
All calculations use established mathematical formulas and are performed with high-precision arithmetic. Results are accurate to the precision shown. For critical decisions in finance, medicine, or engineering, always verify results with a qualified professional.