SEISMIC Archives - QuakeLogic

Choosing the Right Seismometer: Why One Size Doesn’t Fit All

Seismology and geophysical monitoring cover an enormous frequency spectrum — from the fast, high-frequency vibrations of a blast or building resonance to the slow “hum” of Earth itself. No single seismic sensor can capture this entire range with equal fidelity. That’s why different instruments exist, each optimized for a specific corner frequency, bandwidth, and application.

In this article, we explore when to use sensors with response corners at 4.5 Hz, 1 s, 2 s, 10 s, 30 s, 60 s, 120 s, and ultra-long 360 s, highlighting their strengths, weaknesses, and specific use cases. We also explain why one sensor cannot be used universally across all monitoring needs.

Quick Comparison of Seismic Sensors

Sensor Type	Frequency Range (Approx.)	Pros	Cons	Typical Applications
4.5 Hz Geophone	4.5 Hz – 100+ Hz	Low cost, rugged, portable, sensitive to high frequencies	Poor at long-period (>1 s), limited dynamic range	Earthquake engineering, structural monitoring, induced seismicity, aftershocks, MASW/ReMi, site surveys
1 s Sensor	1 Hz – 50 Hz	Good compromise between local & regional coverage, handles ambient noise	Limited for very long-period (>30 s)	Regional seismicity, volcano monitoring, EEW, ambient noise tomography, extended ReMi
2 s Sensor	0.5 Hz – 50 Hz	Captures regional & surface waves up to ~50 s, cost-effective	Insufficient for very long-period (>100 s)	Regional networks, subduction monitoring, passive seismic surveys
10 s Broadband	0.1 Hz – 50 Hz	Versatile, reliable for most teleseismic and regional studies	Cannot resolve very long-period oscillations (>120 s)	National seismic networks, crustal/mantle imaging, hazard assessment
30 s Broadband	0.03 Hz – 50 Hz	Extends into long-period surface waves	More noise-sensitive, higher cost	Global seismology, tomography, moment tensor inversions
60 s Broadband	0.016 Hz – 50 Hz	Excellent for large earthquake teleseisms, free oscillations	Overkill for regional/local studies, needs quiet vaults	Global networks, nuclear test monitoring
120 s Broadband	0.008 Hz – 50 Hz	Full-spectrum coverage, ideal for global networks	Expensive, requires special installation	GSN stations, large earthquake research, planetary seismology
360 s Ultra-Broadband	0.003 Hz – 50 Hz	Captures Earth’s hum, seismic tides, geodynamics	Niche, very noise-sensitive, costly	Geodynamic observatories, tidal studies, climate-related mass transport

4.5 Hz Sensors (Short-Period Geophones)

When to use:

Local earthquake detection (within tens of kilometers).
Engineering and structural health monitoring.
Microseismicity, quarry or mine blasts.
Geophysical testing (MASW, ReMi, refraction/reflection).

Pros:

Rugged, portable, and low cost.
High sensitivity to high-frequency ground motions (>5 Hz).
Excellent for near-field strong-motion recording.

Cons/Limitations:

Poor sensitivity below ~1 Hz, cannot capture long-period seismic waves.
Unsuitable for regional and global/teleseismic events.
Limited dynamic range compared to broadband instruments.

Typical Applications:

Earthquake engineering, dam or bridge monitoring, induced seismicity, aftershock arrays.
Geophysical surveys such as MASW (Multichannel Analysis of Surface Waves for shallow Vs profiles), ReMi (Refraction Microtremor passive site characterization), and seismic refraction/reflection studies.

1 s Sensors

When to use:

Regional seismicity (hundreds of kilometers).
Strong-motion networks where both local and regional signals matter.
Volcano and microseismic monitoring.
Urban geophysical studies using ambient noise.

Pros:

Balanced response between short-period and moderate-period signals.
Captures both body waves and surface waves up to ~20–30 s.
Suitable for passive array surveys (extended ReMi, microtremor analysis).

Cons/Limitations:

Insufficient for very long-period (>30 s) surface waves.
Less sensitive to teleseisms than true broadband sensors.

Typical Applications:

Regional earthquake catalogs, EEW systems, volcano observatories.
Ambient noise tomography, urban microzonation, extended ReMi studies for deeper shear-wave velocity profiling.

2 s Sensors

When to use:

Regional to teleseismic earthquakes.
Arrays where both body and surface waves are important.
Cost-sensitive networks needing extended bandwidth.

Pros:

Wider bandwidth than 1 s, capable of recording surface waves up to ~50 s.
Good compromise between cost and performance.

Cons/Limitations:

Not sufficient for very long-period (>100 s) phenomena.
Still more noise-sensitive than longer-period broadband sensors.

Typical Applications:

Regional seismic monitoring, tectonic studies, subduction zone networks.
Passive seismic surveys requiring both regional and long-period information.

10 s Sensors

When to use:

General-purpose broadband seismic networks.
Regional and teleseismic earthquake detection.

Pros:

Industry standard broadband response.
Sensitive to both surface and body waves.
Reliable and versatile for many applications.

Cons/Limitations:

Cannot resolve very long-period (>120 s) free oscillations.

Typical Applications:

National networks, crustal imaging, mantle tomography.
Earthquake source characterization and hazard assessment.

30 s Sensors

When to use:

Long-period surface wave studies.
Subduction and mantle structure investigations.
Broadband observatories.

Pros:

Extends useful response to long-period surface waves.
Stable in low-noise environments.

Cons/Limitations:

Higher cost and more complex installation.
Susceptible to cultural and wind noise.

Typical Applications:

Tomography, global seismology, moment tensor inversion.

60 s Sensors

When to use:

Large earthquake teleseisms.
Long-period mantle and core phase recordings.

Pros:

Excellent for large-magnitude earthquakes.
Sensitive to Earth’s free oscillations.

Cons/Limitations:

Over-engineered for local or regional seismic monitoring.
Requires very quiet installation sites.

Typical Applications:

Global seismic networks, nuclear test monitoring, Earth structure studies.

120 s Sensors

When to use:

Global seismology, full spectrum earthquake monitoring.
Earth’s free oscillations and tidal studies.

Pros:

Covers almost the entire seismological band (0.008–50 Hz).
Critical for large, distant earthquakes.

Cons/Limitations:

Expensive, complex, vault installation needed.
Not practical for engineering-scale or high-frequency studies.

Typical Applications:

GSN (Global Seismographic Network), Earth structure research, planetary seismology.

360 s Sensors (Ultra-Long-Period Broadband)

When to use:

Recording Earth’s “hum” and seismic tides.
Geodynamic monitoring of slow, long-period processes.

Pros:

Extends response into tidal and ultra-long-period bands.
Captures signals invisible to conventional broadband sensors.

Cons/Limitations:

Highly sensitive to environmental noise.
Costly and niche, requiring ultra-quiet observatory conditions.

Typical Applications:

Geodynamics, glacial isostatic adjustment, climate-related mass transport studies.

Why One Sensor Can’t Do It All

Frequency Trade-Offs: A sensor tuned for high-frequency microseismic signals cannot also detect Earth tides and free oscillations.
Dynamic Range: Instruments designed for small ambient noise may clip during strong shaking.
Installation & Cost: Ultra-broadband sensors need expensive vaults and isolation, while geophones are portable and inexpensive.
Application-Specific Needs: Engineering, geophysics, regional monitoring, and global seismology each demand different spectral coverage.

Conclusion

The “best” seismic sensor depends on what you want to measure.

4.5 Hz geophones dominate in engineering seismology, structural monitoring, MASW, ReMi, and site investigations.
1–2 s sensors bridge the gap for regional seismicity and passive geophysical surveys.
10–120 s broadband sensors are the backbone of national and global seismic networks.
360 s ultra-broadband sensors are specialized tools for studying Earth’s slowest processes.

Seismology is broadband by nature, but practice demands choosing the right tool for the job.

At QuakeLogic, our experts can help you for selecting the right seismometer for your application.

To explore our range of seismometers, visit us at https://products.quakelogic.net/seismometers/

Galperin vs Orthogonal Seismometer Configurations: What’s the Difference and Why It Matters?

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.

DAM FAILURES IN MIDLAND, MICHIGAN – WHEN A DISASTER HITS, WILL YOU BE PREPARED?

15 Jan 2024
QuakeLogic
Blog
Comments Off on DAM FAILURES IN MIDLAND, MICHIGAN – WHEN A DISASTER HITS, WILL YOU BE PREPARED?

When disaster strikes, we are all at risk! But the unprepared ones get hit the hardest.

The Edenville Dam collapsed and the Sanford Dam was breached in Midland, Michigan on last Tuesday (May 19) after days of heavy rain. In the midst of the Coronavirus pandemic, residents were ordered to evacuate because of rising waters. The collapsed Edenville Dam, built-in 1924, was rated in unsatisfactory condition while the Sanford Dam, which was built in 1925, was given a fair condition rating by the state.

Are other dams safe in the US?

On average, the nation’s dams are over 50 years old. At least 1,680 dams across the U.S. are currently rated in poor or unsatisfactory condition. These all pose potential risk according to this Associated Press article. Without urgent action, aging dams may not be able to adequately handle the intense rainfall and floods of a changing climate, as happened in the case of the Michigan dams. They may fail to protect people and property in cities and towns located nearby and downstream.

Introducing SMART DAMS

QUAKELOGIC is the only company using a cloud-based, AI-powered technology platform to perform continuous, autonomous structural assessments using data from sensors on the dam structure.

Deploying the QuakeLogic’s SENSOR DATA MANAGEMENT, ASSESSMENT, AND REPOSITORY TECHNOLOGY (SMART) on dams would significantly reduce needed search and inspection efforts in future events.

The SMART integrates manually and digitally read sensor recordings into a fully-automated unified monitoring system. It facilitates the acquisition and analysis of critical sensor data needed by the dam operators for proper operations and maintenance, and most importantly for the safety assessment of the dam.

The SMART helps to collect, organize, and evaluates sensor data routinely, sends immediate notifications upon exceedance of thresholds, and generate PDF reports regularly and on-demand.

The SMART is a cutting-edge system works with various types of sensors such as accelerometers, tiltmeters, potentiometers, strain gauges, thermocouples, weather stations, piezometers and seepage monitors. Comprehensive analytic information is visible in real-time on the mobile-friendly dashboard, providing proof and peace of mind that a dam is performing as expected.

In addition to SMART, our proprietary earthquake early warning (EEW) alerts provide a window of opportunity for action before earthquake shaking begins at the site. It can also trigger automated actions such as opening spillways, closing roads, etc. when every second counts.

Easy-to-understand, engineering-quality information about the real-time health of the dam supports operators to make informed decisions. Whether planning maintenance activities, or prioritizing critical response actions, QUAKELOGIC has you covered.

“Dams are vital in all communities. As we move toward recovery from COVID-19, it’s important to support the resiliency of dams by realtime monitoring and ensure that the dam owners have the support, tools, and resources to outsmart disasters.”