ESP32-seismometer

Real time seismometer using MPU6050/MPU9250

Realtime ESP32-seismomter by MPU6050/MPU9250 with BMP388 barometer

This program is a personal experiment to measure realtime Japan Meteorological
Agency(JMA)’s instrumental seismic intensity scale (Shindo) with simplified
algorithm, not fully following the procedures defined in reference [2].

No warranty for the precision of the intensity scale provided by this program.

Shindo (JMA’s instrumental seismic intensity scale ) is only used in Japan and it is different from MSK or MM scale.[1]

About Shindo (JMA’s instrumental seismic intensity scale )

  • Shindo 2.5-3.4 is around 6-20 gal. Frequently observed in Japan.
  • Shindo 3.5-4.4 is around 20-60 gal.
  • Shindo 4.5-4.9 is around 60-110 gal. Get ready to protect yourself.
  • Shindo 5.0-5.4 is around 110-200 gal. I have experienced this on the 14th floor in March 11th,2011. Extremely scary earthquake!

Shindo(Instrumental seismic intensity) and acceleration is quoted from [3].
Up to Shindo 2 is a noise level observed by this system.

How to get Shindo (IfF)

IfF (Shindo: Instrumental seismic intensity scale by JMA ) is by definition,

    IfF = 2.0 * log10( af ) + 0.94 

where “af” is acceleration in gal,
after filtering in the frequency domain for the entire time span using specified filter by JMA [2].

Fig.1

Max “af” acceleration corresponds 0.3sec duration is used to calculate max IfF for the entire shake. [2]

For example , IfF[]={3.2 , 1.2 , 2.5 , 2.2 , 3.1} is observed every 100msec
, then let sort these values to {3.2,3.1,2.5,2.2,1.2} and the third value 2.5 is the max IfF Shindo for the earthquake.

Realtime IfF

Procedure [2] should be done for the entire waveform of the acceleration vector
, but this program provides realtime IfF using a sliding buffer of 3 sec (30 samples) and
simplified digital low pass/high pass filter in the time domein.

Since the filter in frequency domain specified in [2] is not easy to implement,
software high pass filter at 0.2Hz and lowpass filter at 5Hz
from sampling interval 10Hz are used to mimic the filter curve defined in [2].
High pass filter by Filters.h [5] also removes the gravity (980 gal), thanks to [4].

In this program , IfF at every 100msec are held for 3 sec in the sliding buffer
(30 samples) and sorted every 100msec to find the third highest value, corresponding to 0.3sec rule in [2]. (thanks to ArduinoSort[7])

Max IfF during the last 30 sec is latched and published to MQTT server as Json format data, expecting
Thingsboard running at MQTT port=2883 visualizes the Json data.( Note: default thingsboard opens port=1883 )
IfF_h is also calculated from horizontal acceleration.

Json format : {"press1": 1023.12,"temp1": 12.5,"IfF": 2.51 , "IfF_h":2.31}
  • press1: barometric pressure in hPa from BMP388
  • temp1: temperature in C from BMP388
  • IfF: seismic intensity from 3D acceleration
  • IfF_h: seismic intensity from horizontal acceleration

Fig.2

Acceleration is measured by MPU6050/MPU9250 placed horizontally.
Since earthquake or volcanic erruption may affect barometric pressure , BMP388 is attached.
Both devices are connected via I2C bus. If BMP388 is not attached , this program only
sends IfF and IfF_h.

Fig.3 view by Thingsboard

Simulation

Simulation earthquake data BCJ-L1 and BCJ-L2 are available as an Exel format data from [8].
BCJ data is 10msec interval, one dimensional data , so the simulation data is given to X,Y and Z axis (half of X axis) at every 10msec.
I have converted it to float bcjL1_wave[] and bcjL2_wave[] and run the simulation by #define SIMULATION

BCJ-L1,BCJ-L2 data are not included in this repository.

data BCJ-L1 BCJ-L2 comment
Shindo IfF=5.5 IfF=6.0 See Ref.[6] page.8
max IfF by this program IfF=5.44 IfF=5.93 for 0.2Hz software high pass filter at sampling rate 10Hz

The result is not bad by chance, real earth quake is not yet observed.

Hardware

  • ESP32devkit

  • GY-521 MPU6050 or MPU9250 board wired on I2C bus.

  • BMP388(optional) from Adafruit on I2C bus.

         SDA = GPIO_NUM_21 , SCL = GPIO_NUM_22
         LED and appropriate resister at GPIO_NUM_2 to indicate WiFi is ready
    

Bluetooth Serial monitor

Bluttooth serial: acceleration(cm/s2) and IfF can be monitered by Bluetooth Serial terminal as “Seismo-BT-serial”.
Huge partition scheme in Arduino IDE is recommended when #define BTSERIAL is on.

Development environment

Arduino board manager 1.0.6 / Arduino IDE 1.8.19

References

Filters library

BMP388 library

PubSubClient

MQTT server with visiualization tools

License

  • Copyright 2022 by coniferconifer
  • Apache License

Appendix

Fig.4
Barometric pressure surge by Tonga eruption in 20:39 Jan 15,2022 JST by AIRBENTO’s BMP180.
The shock wave traveled 8000km from Tonga to Japan.

GitHub

View Github