In seismic monitoring, triaxial seismometers are essential tools that capture ground motion in three dimensions. But not all triaxial sensors are designed the same way. Two dominant configurations exist: the orthogonal layout and the Galperin symmetric design. Understanding the difference between them is key when deciding how to choose a broadband seismometer or designing your seismic network.
Orthogonal Configuration: The Traditional Layout
Orthogonal seismometers use three sensing elements aligned at right angles:
- X-axis (East-West)
- Y-axis (North-South)
- Z-axis (Vertical)
This configuration provides direct and intuitive measurements of ground motion along geographic axes. It is commonly found in strong-motion sensors and legacy seismic stations.
Pros:
- Simple and direct mapping to geographic directions
- Standard format for data processing
- Useful in structural monitoring when orientation is controlled
Cons:
- Requires precise alignment to true North and level installation
- Uneven horizontal sensitivity
- Prone to increased cross-axis coupling due to asymmetry
Galperin Configuration: The Modern Symmetric Design
First introduced by Evgeny Galperin, this configuration uses three identical sensors, each spaced 120° apart and tilted equally from vertical (typically ~35.26°). Rather than directly measuring along X, Y, and Z, these sensors capture intermediate components. Standard vertical and horizontal motion is then reconstructed through a simple mathematical transformation.
Galperin geometry forms the basis of modern broadband seismometers, including all broadband seismometers offered by QuakeLogic.
Pros:
- Isotropic azimuthal sensitivity for uniform horizontal response
- Mechanically balanced and compact design
- Easier installation — no need for precise geographic orientation
- Ideal for low-noise, high-fidelity broadband recording
- Often includes self-leveling mechanisms
Cons:
- Requires post-processing to derive standard components (Z, N, E)
- May be unfamiliar to users expecting direct XYZ outputs
Coordinate Transformation in Galperin Systems
The raw sensor outputs (V1, V2, V3) from a Galperin layout are converted into vertical (Z) and orthogonal horizontal (X, Y or N, E) components through a transformation matrix. The result is functionally identical to orthogonal output — but with superior mechanical and dynamic performance.
To obtain standard seismic components — vertical (Z), north (N), and east (E) — from a Galperin-configured broadband seismometer, a mathematical transformation is applied to the raw outputs of the three equally tilted sensors.
Galperin sensors are mounted 120° apart in azimuth and tilted at approximately 35.26° from vertical. This symmetric geometry ensures equal sensitivity in all horizontal directions, making it ideal for high-fidelity broadband seismic recording.
The transformation to orthogonal components is handled by a fixed matrix derived from the Galperin geometry. Here’s a practical example in Python that demonstrates how to convert the raw Galperin outputs (V1, V2, V3) into Z, N, and E components:
import numpy as np
def galperin_to_orthogonal(V1, V2, V3):
"""
Transforms Galperin outputs (V1, V2, V3) into orthogonal components (Z, N, E).
Assumes Galperin sensors are tilted 35.26 degrees from vertical and 120 degrees apart in azimuth.
"""
# Galperin angle in degrees and radians
alpha_deg = 35.2643897 # approximately arccos(1/sqrt(3))
alpha_rad = np.radians(alpha_deg)
# Transformation matrix based on Galperin geometry
# Source: Galperin 1985; commonly used form
T = np.array([
[np.cos(alpha_rad), np.cos(alpha_rad), np.cos(alpha_rad)], # Z (vertical)
[np.sin(alpha_rad), -0.5 * np.sin(alpha_rad), -0.5 * np.sin(alpha_rad)], # N (North)
[0, np.sqrt(3)/2 * np.sin(alpha_rad), -np.sqrt(3)/2 * np.sin(alpha_rad)] # E (East)
])
# Stack Galperin outputs into column vector
V = np.array([V1, V2, V3])
# Perform transformation
Z, N, E = T @ V
return Z, N, E
# Example usage
V1, V2, V3 = 0.1, 0.2, 0.15 # Example raw sensor outputs
Z, N, E = galperin_to_orthogonal(V1, V2, V3)
print("Vertical (Z):", Z)
print("North (N):", N)
print("East (E):", E)
This code is useful for researchers, engineers, or software developers integrating Galperin seismometers into their own data acquisition systems or post-processing pipelines.
Why Galperin Excels in Broadband Performance
Galperin-configured sensors offer lower cross-axis sensitivity, reduced internal noise, and azimuthal symmetry. This makes them particularly suited for high-precision seismological research.
Optimizing Your Network Design
Because Galperin-based instruments don’t require precise geographic orientation, they simplify field deployments and reduce installation error. This is especially helpful in large-scale projects and remote installations.
✅ QuakeLogic’s Seismometer Solution
At QuakeLogic, we exclusively offer Galperin-type broadband seismometers, engineered for superior sensitivity, symmetrical mechanical design, and fast, easy deployment. Our systems are:
- Fully turnkey, with no licensing or calibration fees
- Designed for broadband performance with low self-noise
- Delivered with user-friendly software and optional remote monitoring tools
- Compatible with standard seismic analysis workflows
Whether you’re deploying a temporary station or building out a national seismic network, Galperin configuration delivers the performance you need with the reliability you trust.
📞 Contact Us
Ready to upgrade your monitoring system? Reach out to our team at sales@quakelogic.net or browse our product line at products.quakelogic.net to explore QuakeLogic’s advanced broadband solutions.
