EARTHQUAKE ALERTS THROUGH CELLPHONES

ABSTRACT

Every   year   thousands   of   people   die   because   an   earthquake   catches   them   in   a   dangerous place   or during   a   defenseless   sleep.  Earthquake   alerts   through   mobile   services   could   be   more   efficient   and   easier   way   to   approach   a   user.   Telestatistics   predicts   that   there   are   over   51 million   mobile   users   in India. Portability   and   their   inexpensiveness   increase   the   speed and   ways   of   communication. Energy   wave   released   at   the   epicenter   of   the   earthquake   travels slower   (3.5 to 8 km/s)   than   light. Primary (P) waves travel very fast, Secondary(s)-waves   which   are   slower  and  harmful   can   be   predicted   before   striking   based   on   property   that   they   travel   at   a   rate   slower than   Primary (p)-waves. Hence   the   alerts   can   be   sent   before   the   s -waves   reach   the   surface. This   system   uses earthquake   sensor   network,   decision alert  system,   dissemination   system. It simply generates   alert   signals   when   the   level   of   earth   vibrations   cross   threshold   and   passes   them   to   the users   via   SMS   services.   SMS   server   can   send   messages   at   the   rate   40 messages/second,            and   the   time   lapse   for   taking   up   the   precautions   would   be   60  seconds,   which   are   enough   to   take   precautionary   steps   like   stopping   the   speed   trains,   busses,   to   run   away   from   poorly constructed   buildings.  The   possibility   of   false   alarms   is   also   reduced   as   the   information   is verified   thoroughly. Using   this   complete   safeguard   against   earthquakes   cannot   be   assured   but the   number   of   causalities   could   be   reduced   by   taking   necessary   penultimate   steps.

INTRODUCTION:

               Earthquakes  strike  without  warning .The  resulting   damage   can   be   minimized   and   lives   can be   saved, if   the   people   living   in   the   earthquake - prone   area   are   already   prepared   to survive   the   strike. This   requires   a   warning   before   the   strong   ground   motion   from the   earthquake arrives. Such   a   warning   system   is   pos­sible   because   the   energy   wave   released   at   the   epicenter   of   the   earthquake   travels   at a   rate   slower   (at 3.5 to 8 km/s)   than   light.

               The   warning   signal   from   the   earth­quake   epicenter   can   be   transmitted   to   dif­ferent   places   using   the   satellite   communi­cation   network, fiber –optics   network, pager service, cell phone   service   or   a   combina­tion   of   these. The   satellite-based   network   is   ideal if   the   alert   system   has   to   cover   a   large   country   like   India.

                For   earthquake-prone   states   like   Gujarat, a   seismic   alert   system   using   the   global   system for   mobile   communication (GSM)   network   spread   throughout   the   state is   proposed   here. This   system   does   not   try   to   find   the   epicenter   or  the   fault   line   caused   by   the earthquake. It   simply   monitors   the   earth   vibrations   and   generates alert   signal   when   the   level of   earth   vibrations   crosses   a threshold.

                After   receiving   alert,   a   middle-aged   person   takes 30 to 40   seconds   to   go   down   the   stairs  from   fifth   floor  . If   it   takes   a   minimum   of   10 seconds   to   damage   a   poorly   structured   house,   these 10 seconds   too   can   be   considered   for going   to   safer   place. If   we   consider   these   points, giving   earthquake   alert   before   the   actual occurrence   of   earthquake   can   minimize casualties.

EARTH QUAKES:

 A sudden, transient motion or trembling of the earth's crust, resulting from the waves  in  the  earth  caused by faulting  of the rocks or by volcanic activity.

P-WAVES & S-WAVES:-            

                         When  an   earthquake  occurs,  it  releases  energy  in  the  form  of  waves  that  radiate from  that  earth- quake source in  all  direc­tions. Different  types  of  energy  waves shake  the  ground  in  different  ways and  travel  through  the  earth  at  different  ve­locities. The  fastest  waves  are  called  pri­mary (P) waves. These  are  compressional in nature like sound  wave, and  compress  and  expand  material  in  their direction  of  travel. P  waves  move  at  a  speed  of  8    km/second. These waves  are not destructive  in  nature.                                                                                                                                                                                 

            

p-waves     & s-waves

           Secondary (S)   waves   have   the   charac­teristics   similar  to  the  waves  on  the  sur­face of  water. These  move  the  earth  up  and  down  perpendicular  to  the  direction  of  their  motion. S waves are slower than P waves, moving at half the velocity of P waves (4 km/second). Vertical ground motion generated by S waves is highly damaging to the structures.

LOVE AND RAYLEIGH WAVES:-

           However most structural damage is caused by surface waves that are slower than S waves, called Love and Rayleigh, these waves shake the ground hori­zontally .Destruction also depends on the frequency of ground vibrations. P and S waves have higher frequency of vi­bration, which shakes the low-rise buildings. The Love and Rayleigh waves have less than 1Hz vibrations, which cause high rise buildings to vibrate.     

Since slower waves which have more damaging characteristics reach distant places from epicenter much later, alerts could decrease the causalities. Among the various possible alerts like alerts through radios, television, internet etc, SMS alert through cell phones have following advantages.

ADVANTAGES OF CELL PHONES OVER OTHER SERVICES:

1.Telestatics predicts that India’s cell phone subscribers are increasing exponentially everyyear

According  to  the  survey, the  number  of  cell  phone  subscribers in India are  51  millions.

2. They are small and portable. Thus even if user is away from city or on his journey, he  would   get an  alert signal.

3.It is the faster means of transmitting the messages.

4.Cell phones have full duplex. This means that you can use one frequency for talking and a second frequency, separate frequency for listening. Both people on a cell phone can talk at once.

COMMUNICATING THE DANGER:

This GSM-based alert system monitors the earth vibration using a strong motion ac­celerometer at the earthquake-prone area and broadcasts an alert message to towns and villages through the cellphone net­work existing throughout the state. Here mobile phones are used as transmitters  and receivers.

The communication system for earth­quake alert comprises an earthquake sen­sor and interface unit, decision system and alert –dissemination network.

1Short message service:

             The short message service (SMS) of the GSM network allows one to send a message consisting of a maximum of 160 alphanumeric characters to or from a mobile station. This service can be viewed as an advanced form of alphanumeric paging with a number of advantages. If the subscriber's mobile unit is powered off or has left the coverage area, the message is stored and offered back to the subscriber when the mobile is powered on or has re-entered the coverage area of the network. This ensures that the message will be received.

2Earthquake-sensor Network: 

                Earth­quake sensors (strong motion accelerom­eters) are deployed at known epicenters (20 to 30 in numbers only for Gujarat), fault line zones and earthquake-prone areas. Earth­quake-prone areas like Bhuj may have sen­sors at more than two or three places, located 40 to 50  km away from each other.

Each sensing location should have two accelerometers placed two to three meters away from each other. The purpose of installing two accelerometers at each place is to detect and eliminate the local vibra­tion noise, which can give false signals (vibration) to the accelerometer. An inter­face unit, which has to be developed, will monitor both the accelerometers. It will act only when both the accelerometers give the same signals.

Since this is only an alert network and does not find out the location of the epi­center, only the discrete magnitude levels will be detected and any magnitude above the preset threshold level will be trans­ferred to the mobile receiver handset via short message service (SMS). The hand­set, in turn, will transfer it to the base transceiver stations (BTS) if it is within 10 to 17 km of the BTS. Otherwise, it may require a repeater for transferring data to the cellphone network.

The handset should have auto-dialling facility and be preloaded with a fixed di­alling number and fixed message. When­ever the handset gets a signal (pulse) from the interface unit, it goes into the auto­dialling mode and transfers data to the network and waits for the next pulse with the same number and message.

3Decision system:

              When an SMS is sent from the mobile handset, it first goes to the SMS server of the mobile network, then to the destination receiver handset. If the same message has to be sent to different locations (receivers), the trans­mitter handset has to dial different num­bers for different destinations.

But in this proposed system, on a single transmission the message should go to different predefined locations.

This is possible if the SMS server of the mobile network is programmed for such a facil­ity. In fact, this type of facility already exists in the GSM network in the form of 'cell broadcast.' But it is not advisable to disturb the main server specially for this system. Another application server may be included in the network for the alert system, which will work as the interface between the network (SMS) server and the transmitter located at different earth­quake-prone areas or epicenters.

4 Interface Unit:

             At the epicenter, the interface unit trig­gers the handset as soon as it receives P and S waves of the predefined magnitude. The handset is always ready with the fixed message and destination number. Here the destination is the application server, which has been included for the proposed sys­tem and should be connected to the SMS server of the mobile telephony (GSM) net­work. It also acts as an interface between the single source transmitter (epicenter) and multiple receivers installed at differ­ent towns and villages.

All the source handsets (placed at different locations for sending the alert messages) should be registered at the application server. As soon as the appli­cation server receives an alert message (through the SMS server) from a particu­lar registered source handset or transmit­ter, it first  checks whether it is for P wave or S wave.

                  An epicenter will first send P wave, then S wave after a few seconds. Therefore the application server should  know from the first message transmission that it is P wave and from the second message that it is S wave. Accordingly, it looks for the respective look-up table that contains destination-dialing numbers and passes the same to the SMS server. The SMS server sends alert messages at the rate of 40 mes­sages per second (maximum capacity of the existing mobile phone network) to all the destinations through the GSM network. Therefore in this mode it takes a maximum of only one second for sending the  alert signals to the predefined destinations.

                   As mentioned above, the application server should have look-up tables for alert messages of P and S waves. For example, if an earthquake sensor  detects P  wave of the preset magnitude and an alert message is sent to the appli­cation server through the network, the application server looks for the look-up table for the numbers it has to dial. As P wave is detected earlier than S wave, it will send alert-signals to the nearby towns and villages within the range of 50 to 100km.This will take 2 or 3 seconds.

              After a few seconds, the application server will receive another alert message from the same epicenter. It counts this as the message for S wave-this also confirms the earthquake.­The application server again goes through the look-up table to send the alert signal to different loca­tions within 50 to 100 km. Since earthquakes of a magnitude less than 5.5 on Richter scale hardly affect the buildings, this system is designed to start sending alert signals if the earthquake mag­nitude is more than 5.5 on Richter scale. The magnitude threshold for sending the alert signals can be decided by an ex­perts' committee.

                      If earthquake sensors at different epi­centers are placed 40 to 50 km apart, an earthquake at a particular epicenter will hit the other sensors as well after a few seconds be­cause earthquake waves move at around 3.5 and 8 km/second. Consequently, other interface units will also start sending (through the dial network) alert signals to different locations as per the look-up table given in the application server. Therefore destination locations will get alert signals every few seconds, which confirms that a destructive earthquake wave is moving on the earth from one place to another.

5 Alert-dissemination network: 

                 As men­tioned earlier, the alert-dissemination net­work is a simple cell phone network (GSM) in SMS mode, which already exists in most of the states in India. Alert messages are transferred to the destination handset through the mobile network system in SMS mode. The receivers are installed at differ­ent places as individual units or in groups. These should have an interface unit to read the message and take action to disseminate the alert message to the public. The alert receivers could be attached to the civil defense sirens and broadcast systems, and  also installed at government offices that are responsible for disaster management.

TIME-TO-ALERT:

                In this system, time-to-alert is the time between the actual occurrence of the earthquake at the sensing point and the audio or text message output at the pub­lic or government offices. End-to-end com­munication delay will be very less, pro­vided all the transmitters (handsets) placed at different epicenters are given the top priority for communication in SMS mode. For this, a permanent instruction (through the application server) has to be given to the SMS server of the communication network so that whenever an alert mes­sage comes from the identified locations (registered to the application server), the server gives it the top priority and trans­mits it to the destination immediately.

               Time delay at the sensor location in­cludes the sensor (accelerometer) response time, circuit delay and processing time at the interface unit to form the alert signal. At a few tens of milliseconds, this is neg­ligible.

               Time to transfer the alert signal from the epicenter to the application server will be a maximum of three seconds because the SMS server will give priority to this message.

Once the alert signal (message) is formed, the interface unit will transfer it to the transmitter. The transmitted mes­sage will be received by the application server, then forwarded to the SMS server. The SMS server will transfer the SMS mes­sage at the rate of 40 messages per sec­ond. The worst-case sum of the time taken by all these components is five to six sec­onds for a particular region only.

ADVANTAGES OF THE SYSTEM

• Audio alarms can be installed to alert people, but the action that individual can take with only a few seconds of warning may be minimal. Facilities with high-energy or high-precision machinery (nuclear power plants, airport operations, computers, oil pipelines, refineries and gas distributions) could be shut down.
• Trains could be stopped.Fire stations and hospi­tal operation rooms alerted, and emergency generators started. 
• As a poorly structured building takes at least five seconds to collapse, three sec­onds spent in transferring the S-wave alert signals to the SMS server can still give enough time to seek safety
• Alarming the population living in the downstream region of a large dam  would be helpful.
• The cost of an earthquake early warning system is low compared to other measures (improvements of rolling stock, rail/track system, embankments, tunnels, bridges etc.).

CONCLUSIONS

This earthquake alert system senses earth­quake waves at potential earthquake zones, transmits these discrete magnitude values to a central place via GSM cell phone network, and uses computer-based deci­sion making to deliver alert signals to the identified receivers placed at different towns and cities for both public and gov­ernment consumption.

The system is simple and could be configured with available resources in the country. Here, only concepts are described. Detailed simulation, feasibility study and experimentation are required to optimise the system and reduce the possibilities of  false alarm.