1. iShake: Mobile Phones as Seismic Sensors
Shideh Dashti, Jack Reilly, Jonathan Bray, Alexandre Bayen, Steven Glaser, Ervasti Mari
U.C. Berkeley
Funded by the US Geological Survey under NEHRP Award G10AP00006
Acknowledgements:
UC San Diego and UC Berkeley Shaking Table facilities
Special thanks to Professor Mahin at UC Berkeley and Professor Hutchinson at UC San Diego
Good morning, it’s a pleasure to be here.
I’m going to talk about the iShake project on the use of mobile phones as seismic sensors.
Before I start, I would like to thank the individuals who made this research possible. First Jack Reilly, the graduate student researcher on this project, and the principal investigators were Professors Bray, Bayen, and Glaser at UC Berkeley, and Mari Ervasti a visiting scholar from Finland working on the user interface side of the project.
This project was funded by the USGS and I would like to acknowledge the staff at the UCSD and UCB Shaking Table Facilities and particularly professors Mahin at Berkeley and Hutchinson at UCSD for their assistance.

2. Post-Earthquake Information
UC Berkeley Shideh Dashti
Saturday, April 22, 2017
Post-Earthquake Information
ShakeMap
M=7.2 Baja California EQ from USGS (2010)
Emergency responders must “see” the effects of an earthquake clearly and rapidly so that they can respond effectively to the damage it has produced. Great strides have been made recently in developing methodologies that deliver rapid and accurate post-earthquake information. Examples of successful existing products are the USGS high quality shake intensity map (that David discussed in his very interesting presentation) and… …
you see that you have good definition where there are stations and poor definition where there are not stations. While it does contain algorithms for estimating ground motions in areas of sparse station coverage through interpolation and use of rapid finite-fault analyses, which include generalized site amplification, its reliability is hindered directly by the limited number of high quality instruments available.
USGS 2

3. Post-Earthquake Information
UC Berkeley Shideh Dashti
Saturday, April 22, 2017
Post-Earthquake Information
Community Internet Intensity Map (CIIM)
M=7.2 Baja California EQ from USGS (2010)
Emergency responders must “see” the effects of an earthquake clearly and rapidly so that they can respond effectively to the damage it has produced. Great strides have been made recently in developing methodologies that deliver rapid and accurate post-earthquake information. Examples of successful existing products are the USGS high quality shake intensity map (that David discussed in his very interesting presentation)
and the “Did You Feel It?” community based project, which depends on people to observe and respond and provides a sense of the intensity of shaking, as a first approximation. A single MMI is assigned to a zip code and zip codes that have no response are shown as gray here.
USGS 3

4. Post-Earthquake Information
UC Berkeley Shideh Dashti
Saturday, April 22, 2017
Post-Earthquake Information
“Did You Feel It?” or Community Internet Intensity Map (CIIM)
ShakeMap
Emergency responders must “see” the effects of an earthquake clearly and rapidly so that they can respond effectively to the damage it has produced. Great strides have been made recently in developing methodologies that deliver rapid and accurate post-earthquake information. Examples of successful existing products are the USGS shake intensity map, which is mostly based on high-quality instrument measurements.
and the “Did You Feel It?” community based project, which depends on people to observe and respond based on sense of the intensity of shaking, which David just discussed in his great presentation. …
Note the differences in the CIIM and ShakeMap portrayals of the 2010 Baja California Earthquake.
The resolution of ShakeMap depends on the number of stations in a given area and the availability of low quality but useful data in DYFI-map depends on what zip codes are represented.
M=7.2 Baja California EQ from USGS (2010) 4

5. ? accuracy UC Berkeley Shideh Dashti Saturday, April 22, 2017 5
However, shortcomings still exist.
There is a gap between the high quality, but sparse, ground motion instrument data that are used to help develop ShakeMap and the low quality, but sometimes larger quantity, human observational data collected to construct a “Did You Feel It?” (DYFI)-based map.
Let’s have a show of hands for people who have smartphones? Ok…
Our goal is to use your smartphones to bridge this gap.
Rather than relying on individuals’ feedback as our measurement “devices” sometime after the earthquake, in the iShake project we use their cell phones to measure ground motion intensity parameters and automatically deliver the data to our servers immediately after the event for processing and dissemination.
In this participatory sensing paradigm, semi-quantitative shaking data from numerous cellular phones might enable the USGS to produce shaking intensity maps more rapidly and accurately than presently possible. …
While the proportion of smartphones remains a minority of the phones in use in the world today, the technology onboard these phones is permeating the fleet of more affordable phones available to the public. Thanks to mass production, the cost of advanced sensors has dropped significantly; for example, the cost of a standard GPS module for a phone presently costs the manufacturer between $1 and $10. Cameras have also become a standard feature of all phones, and it is expected that the incorporation of accelerometers will follow a similar path in the near future.
accuracy 5

6. Training Set Model Prediction Predicted Loose Probability
Sensor Connection Evaluation
Training Set Model Prediction
Moreover, even for phones that are connected to the ground or wall, the connection may be loose. Additional experiments were performed and a probabilistic approach was adopted to determine the phone connection type, using the measured signal.
Actual Loose State
Acceleration (g)
Predicted Loose Probability
Time (s)

7. System Architecture UC Berkeley Shideh Dashti Saturday, April 22, 2017
A client application and backend server was developed, the performance of which needed to be evaluated through experiments and field tests. 7

8. iShake Sensor Quality Evaluation Systems Field Tests
Shaking Table Tests
Testing of Phone Connections
Systems
Client Application
Backend Server
Field Tests
User Studies
The scope of the initial phase of the iShake project was to:
1) evaluate the quality of the phone as a sensor
2) Develop the systems architecture, consisting of a client application and backend server, the performance of which needed to be evaluated through experiments and field tests.

9. iShake Sensor Quality Evaluation Systems Field Tests
Shaking Table Tests
Testing of Phone Connections
Systems
Client Application
Backend Server
Field Tests
User Studies
In this presentation, I will mostly discuss the shaking table tests that were performed to evaluate the performance of a class of cell phones, in this case iPhones.

10. Shaking Table Tests
The phone sensor is an imperfect device with performance variations among phones of a given model as well as between models. The sensor in this case is the entire phone, not just the micro-machined transducer inside. Therefore, the quality and reliability of these phones as seismic sensors first needed to be understood.
Even if we can obtain good quality data from these phones, what about the response of phones that are not rigidly connected to the ground and may be on a table during an earthquake? Can we gain valuable information from those phones? How about a phone that falls? How can we detect that in the recorded signal?
To answer these questions, a series of 1-D and 3-D shaking table tests were performed at UCSD and UC Berkeley, respectively.
This is the shaking table at UCSD and here is the phone setup: In each test seven iPhones and iPod Touch devices that were mounted at different orientations were subjected to earthquake ground motions. 3 high-quality seismic accelerometers were mounted next to each phone and on the base platform to provide reference accelerations in orthogonal directions

11. Spectral Acceleration (g)
Input Ground Motions
A suite of 140, 1-D and 3-D realistic ground motions were applied to the base platform during these experiments to study the mobile sensor’s response for a wide range of ground motions.
...
The selected motions for the 1-D shakes shown here, had a combination of near fault events with the forward directivity effect and less intense, strike slip events recorded at a large distance from faults, in order to better study the mobile sensor’s response for a wide range of ground motions.
These earthquake ground motions were primarily selected based on probabilistic seismic hazard analyses for a site in downtown Los Angeles and for the University of California, Berkeley campus, because the methodologies are being developed and tested in California first. The seismic hazard at these two sites was mostly dominated by
5% Damping
Spectral Acceleration (g)
Arias Intensity(m/s)
Period (s)
Time (s)

12. Application Software
For the purposes of recording acceleration data from all the phones at the same time during a shaking table test, an independent pilot application was developed. This client application is able to send and receive commands to and from a server, while the server stores the recorded shakes and displays them to the user on request.

13. Results: Stationary Phones
Acceleration (g)
Fourier Accel. (cm/s)
Reference
Initially, all phones were rigidly mounted to their holders.
Following these experiments, the ground motions recorded by seven phone sensors were compared with the reference to carefully document the differences.
The comparisons show promise in the quality of phone recordings, particularly in terms of estimating PGA, PGV, and PGD for most ground motions.
iPhone
Time (s)
Frequency (Hz)

14. Results: Stationary Phones
Velocity (cm/s)
Displacement (cm)
Reference
iPhone
Time (s)
Time (s)

15. Spectral Acceleration (g)
Response Spectra
5% Damping
The 5% damped acceleration response spectra recorded by the phones compared reasonably well with the reference.
Spectral Acceleration (g)
Frequency (Hz)

16. Spectral Acceleration (g)
Response Spectra
5% Damping
Particularly, when comparing the averaged spectrum of the seven phones. …
These observations are helpful in evaluating the response of the entire phone local array as a seismic sensor.
Spectral Acceleration (g)
Mean phone
Reference
Frequency (Hz)

17. “Goodness of Fit” Bias (log(g)) Period (s)
The “goodness-of-fit” between the acceleration response spectra obtained from the phones and the reference is shown in terms of phone’s bias and uncertainty here.
These plots combine the bias of each individual phone during all the input ground motions in a given experiment as a function of frequency or period. They indicate that the bias is sufficiently low during the period range of interest for most engineering applications (about 0.1 to 1 sec) in both experiments.
Period (s)

18. Arias Intensity Arias Intensity (m/s) Time (s)
In general, however, the phone sensors showed a tendency for over-estimating the ground motion energy and hence, Arias Intensity (Ia).
Arias Intensity (m/s)
Time (s)

20. Quantifying Phone Error
Normalized Prediction Error
Now, stepping back a little bit, to measure the accuracy and consistency of the acceleration-time histories recorded by individual phones let’s look at the normalized mean squared error term, which is an overall measure of the error in the entire time history. The errors appeared to reducd sharply for stronger ground motions.
With the available data, these errors can be statistically evaluated based on key input ground motion properties. A parametric study of these errors will lead to better estimates of key ground motion parameters from a cluster of lower-quality phone measurements.
Peak Ground Accel. (g)
Peak Ground Displacement (cm)
NPE=MSE/PGA2
MSE

21. Phones Allowed to Move Freely
Following the experiments with phones rigidly connected to their holders, additional tests were performed on phones that were allowed to move freely on the shaking table. In a few cases, frictional or rubber covers were used on the phones to minimize sliding or their independent movements.

22. Shaking Table Tests
This is a video of the two phones with frictional covers left freely on the shake table during a strong 3-D shake.
As we can see here, one of the phones that had a less sticky cover moved slightly but for the most part, these covers were successful in minimizing phone’s sliding.

23. Spectral Acceleration (g)
Phones Allowed to Move with Cover
As shown here, the acceleration response of these two phones compared reasonably well with that of the reference. The acceleration amplitudes recorded by this phone, however, were slightly under-estimated due to its minor tendency to slide.
Also overall, the acceleration response spectra compared relatively well.
Acceleration (g)
Spectral Acceleration (g)
Fourier Accel.
Frequency (Hz)
Frequency (Hz)
Time (s)

24. Phone Allowed to Fall Reference Falling Phone Falling Phone
X-Direction
Reference
Now what if the phone falls? We need to identify and remove its signal from the dataset. So, we tested this by allowing a phone to actually fall during one of the events.
Looking at its response, as expected we see a large spike in the acceleration record. Which was also evident as a sudden increase in the corresponding Arias Intensity-time histories at the time of falling.
This may be used as an initial screening tool to detect the falling instruments and remove them.
Arias Intensity (m/s)
Acceleration (g)
Y-Direction
Z-Direction
Time (s)

25. Phone Allowed to Fall Arias Intensity (m/s) Z-direction
Falling Phone
Arias Intensity (m/s)
Reference
Z-direction
Which was also evident as a sudden increase in the corresponding Arias Intensity-time histories at the time of falling.
This may be used as an initial screening tool to detect the falling instruments and remove them. …
Additional research is underway to better understand the response of falling and moving phones as well as other types of smart phones such as androids.
Acceleration (g)
Time (s)

26. accuracy UC Berkeley Shideh Dashti Saturday, April 22, 2017 26
In conclusion,
When communicating the intensity of shaking with the public and emergency responders after an earthquake, on one side of the spectrum we have the high quality shakemap, the accuracy of which depends on the availability of strong motion stations, and on the other side of the spectrum we have the low quality but potentially high quantity DYFI based maps based on human observations.
accuracy 26

27. UC Berkeley Shideh Dashti
Saturday, April 22, 2017
iShake occupies a third space, as it can provide immediate post-EQ information with a potentially large number of sensors and relatively good quality.
Phones were generally successful in capturing key intensity parameters during shaking table tests.
accuracy 27

28. iShake Application http://ishakeberkeley.appspot.com
If you are interested to be a part of iShake and contribute to this research, please talk to me or Jack after this session for downloading our app on your iPhone or participating in our upcoming field tests in January. In fact the iShake app is available for free download on the app store as of two days ago.