Guidelines for Earthquake Recording Instrumentation

The Gecko SMA-HR was designed with DPWH compliance in mind, with several features engineered specifically to meet the guidelines and implementing rules.
There are many products on the market that claim to be DPWH compliant, but to our knowledge only the SMA-HR and one other much more expensive product actually meet the requirements for monitoring building response to earthquakes.

DPWH Requirement

Gecko SMA-HR Compliance

Information on Requirements

Seismic qualified as tested by recognized international testing laboratory

Sensors and recorders have been tested by the University of Melbourne and University of Technology Sydney. Designer/manufacturer is an ISO 9001:2008 accredited Quality Assurance company.

This ensures your supplier is a manufacturer of real earthquake monitoring equipment, not just a rebranded intensity meter or seismic switch. If you are unsure, check their credentials with PHIVOLCS.

Stores seismic activity information as gathered by the attached accelerometer

Records triaxial data from integrated accelerometer continuously to SD card storage

Be wary of simple seismic switches that do not record waveform data - without recording movement during an earthquake you cannot analyse building response!

Equipped with fault detection

Fault detection logic outputs included in connector port. Data storage, power, and temperature alerts

This allows you to remotely monitor any issues with your accelerographs using a simple circuit breaker output that can be connected to your building control system. Many earthquake accelerographs do not include this feature as standard.

Provides real-time alarm information (either audio, visual or both) during an earthquake event.

Real-time alarm output to relay circuit during earthquake can be connected to audio/visual device

Another uncommon standard feature for an earthquake accelerograph, an local alarm will alert people near the accelerograph, but a more useful feature is to raise this seismic alarm in your building control system. The SMA-HR again uses a simple relay circuit output, either normally open or normally closed.

Equipped with internal battery back-up power to ensure continuous operation during a power fluctuation.

Internal battery gives 12+ hours backup

As earthquake accelerographs are often installed for long periods in remote areas, internal batteries are uncommon, but a small battery to ensure the instrument continues to operate without mains power is a great idea.

Minimum design life: 10 years and should be demonstrated and certified to have a 40,000-hour (minimum) mean time between failures

Designed for minimum 10 year operation. Kelunji SMAs used in structural monitoring have operated for over 20 years: aggregate MTBF of > 5 years

Earthquake accelerograph typically have long model cycles, only renewed every 7-10 years, often operating for 15-20 years or more when installed. Check that your supplier has a proven long term manufacturing history.

Minimum of three components (vertical, longitudinal and transverse)

Three orthogonally aligned accelerometer components (vertical, longitudinal and transverse; East, North, Up)

Vertical channel is important for detecting first motion, horizontals for monitoring the potentially damaging motion.

Natural Frequency: Above 50 Hz

Lowest spurious resonance >450Hz

Most earthquake energy is in the range up to 50Hz, so be sure that the any natural noise from the sensor is above 50Hz

Damping: Approximately 60-70 percent critical

Force feedback sensors have critical damping (100%)

Damping refers to the a physical response of old styles of earthquake seismometers where their springs would bounce for a period of time after being shaken. This is not relevant to most modern accelerometers which use rapid response active circuits.

Sensitivity: 2g

Sensitivity is 5V/g with ±10V range, giving ±2g range

The intention here was to specify the Full Scale Range of the sensor, which should be able to record ±2g: up to twice the acceleration due to gravity, in every direction.

Bandwidth: DC to 100 Hz

Sensor bandwidth is DC to 100 Hz

As mentioned in the Natural Frequency section, most earthquake energy is in the frequency range up to 50Hz, but nearby earthquake can generate higher frequency peaks, so 100Hz is a good buffer.

Environment: IP 67

Compliant with IP67 for dust and water ingression

IP67 means that the accelerometer must be dustproof and is able to be submerged under 1m of water for at least 30 minutes without damage to the sensor. This is particularly relevant to basement accelerographs where flooding is possible.

Sampling Frequency : Minimum of 100 samples per second

Sampling rates up to 4000 samples per second available. 100sps default

Sampling ground motion at 100 samples per second means that you can see signals at up to half that frequency in the data - i.e. up to 50Hz. This is a common sample rate for earthquake monitoring.

Time: From at least 20 seconds before the ground shaking begins until 30 seconds after the last triggering level motion

Data is stored continuously before and after trigger time

Old digital seismographs had limited memory and would only record some time before and after it detected an above-average signal. Modern recorders store data continuously, so extracting any amount of time before or after the detection is possible.

RMS Noise: System noise shall be less than 40µg measured over 0-30 Hz

Measured full spectrum noise is less than 1µg over 0-100 Hz (less than 0.5µg RMS noise over 0-30Hz)

A very important measure of the quality of the sensor and recorder. The system noise should be less than 40µg to be able to detect the small motions of the building at its natural period. Even the best MEMS accelerometers cannot get below 300µg, so be sure to check the sensor technology and noise levels.

Continuous Recording : capable of continuous recording

Continuous recording is always enabled

If you only store triggered events you will not have any data for long term building response analysis. Any modern accelerograph should have the capability to record data continuously.

AD Converter : 16 bits

AD Converter: 32 bits

16-bit analogue to digital converters cannot mathematically achieve 40µg noise levels and also a full scale range of ±2g. The ADC must be at least 18-bits. Modern earthquake accelerographs have 24-bits of resolution.

Interval: Half a second or less

Data storage interval at 100sps is less than 0.5 seconds

Writing data to permanent storage regularly ensures that large data buffers are not stored in volatile processor memory.

Accuracy: Plus or minus 0.2 second per 100 seconds

Time accuracy: 0.00001 seconds, synchronised every second

The timing accuracy of your recorder should be an order of magnitude better than the fastest sampling rate.

Type : GPS or NTP Server

GPS used for timing and position

GPS timing is a globally available timing standard that simply requires a small view of open sky. NTP is only available to devices that have a permanent Internet connection.

Method: Pendulum or other device using earthquake motion as an exciting force

Force feedback circuit. Earthquake motion provides excitation

A pendulum based system cannot be considered for any modern accelerograph. The only technologies that can meet the DPWH requirements are force feedback active coil and optical interferometry accelerometers. MEMS or IEPE accelerometers are simply not sensitive enough for this application.

Level: Accelerograph: 0.5 to 100 gals nominal velocitimeter: 5 μm/s to 1 mm/s

Level triggering for accelerograph any value from 0.2 to 1980 Gal

Acceleration is usually measured in "g" (the force of gravity) which is equivalent to 9.81 metres per second squared (m/s/s). Gal is another unit of acceleration, equivalent to 1 centimetre per second squared (cm/s/s).

Time: Full operation of accelerograph/velocity in not over 0.1 second after activitation.

Full recording operation 100% of time, regardless of trigger activation

Some seismic recorders, usually those designed for blast monitoring, need to suspend recording while writing files to memory. These recorders should be avoided at all costs.

Battery maintained by charger

Battery maintained by AC charger

The charger should automatically resume charging of the battery when mains power is restored, without user intervention.

Ethernet: 10 base –T or 100 base-TX

Ethernet adaptor included

You can connect your accelrographj to a LAN or to the Internet to stream data to a central recording system. In the future DPWH, PHIVOLCS or another authority may host a central data reception system so that your building can be monitored remotely.

Protocol: TCP/IP FTP/SFTP

TCP/IP used over Ethernet/cellular

TCP/IP is a standard Internet Protocol for data communications, enabling data to travel over most systems such as cellular networks, satellite telemetry, fibre and DSL broadband connections.