January/February 2008

The USGS Earthquake Notification Service (ENS): Customizable Notifications of Earthquakes around the Globe

Lisa A. Wald, David J. Wald, Stan Schwarz, Bruce Presgrave, Paul S. Earle, Eric Martinez, and David Oppenheimer
U.S. Geological Survey


At the beginning of 2006, the U.S. Geological Survey (USGS) Earthquake Hazards Program (EHP) introduced a new automated Earthquake Notification Service (ENS) to take the place of the National Earthquake Information Center (NEIC) “Bigquake” system and the various other individual EHP e-mail list-servers for separate regions in the United States. These included northern California, southern California, and the central and eastern United States. ENS is a “one-stop shopping” system that allows Internet users to subscribe to flexible and customizable notifications for earthquakes anywhere in the world. The customization capability allows users to define the what (magnitude threshold), the when (day and night thresholds), and the where (specific regions) for their notifications. Customization is achieved by employing a per-user based request profile, allowing the notifications to be tailored for each individual’s requirements. Such earthquake-parameter-specific custom delivery was not possible with simple e-mail list-servers. Now that event and user profiles are in a structured query lan guage (SQL) database, additional flexibility is possible. At the time of this writing, ENS had more than 114,000 subscribers, with more than 200,000 separate user profiles. On a typical day, more than 188,000 messages get sent to a variety of widely distributed users for a wide range of earthquake locations and magnitudes. The purpose of this article is to describe how ENS works, highlight the features it offers, and summarize plans for future developments.


ENS Features

The ENS interface has many customizable features. The current user interface and options were developed as an iterative process over a period of one year, as feedback was received from a group of beta users. Messages were modified from long-estab lished versions sent by the NEIC and the California Integrated Seismic Network (CISN). Specific details and user configura tion options for each feature are provided on the ENS signup Web page (http://earthquake.usgs.gov/ens/), but in brief they include:

Define geographic region for notification:

Specify your local time zone:

Exclude delivery of aftershocks

Receive notifications for revised earthquake parameters

Specify user affiliation (which determines content of notifications):

Define and manage multiple customized notification profiles

Send alerts to multiple cell/PDA/pager/e-mail addresses

Activate/deactivate each profile individually

Choose from two notification formats:

Language options:

Many of these options were determined based on feedback from users of the NEIC and regionally based systems. Affiliation options can be chosen from a drop-down menu (or by filling in the “Other” box). Scientists receive notifications first, followed by users with emergency response affiliations, because the timeliness of the information is an important factor. The ENS administrator confirms the affiliations before the priorities are set.

The “aftershock exclusion” option allows a user to automatically turn off notifications for all the small aftershocks following a significant earthquake with a prolific aftershock sequence. We have found from experience that many users are overwhelmed with numerous notifications from a sequence of relatively minor aftershocks. If the event is greater than magnitude 5.5, a script queries the database to determine if the event falls within an existing aftershock zone. If there is no prior aftershock zone defined, one is created for the event. The aftershock zone is defined using a hexagon to approximate a circle on the map, centered at the event epicenter, with the radius in kilometers determined by
radius = 10(magnitude – 5) – 5 .

Any subsequent earthquakes within the approximated circle that are more than two units of magnitude below the mainshock magnitude are then flagged as aftershocks, and notifications for those events are not sent to those users who have indicated they want “aftershock exclusion.” The defined exclusion regions are removed automatically from the system by a script that runs once every 24 hours to determine if the event is older than the “aftershock expiration” date, which is based on the magnitude (L. Jones, personal communication, 2006):

The “update notifications” option allows users to indicate whether or not they want to receive notifications when the event solution is updated. Notification updates are sent to those who want them when the location changes by more than 0.5 degree and/or the magnitude changes by 0.3 or more.

The “defer notifications” option determines if the user will receive notifications during the hours specified as “nighttime” for each individual profile. This is an important option to consider for seismologists who want a good night’s sleep. Each profile can be associated with a different magnitude threshold for “day hours” and “night hours.” If the user selects “defer notifications,” then any events over the “day” threshold will be held until morning. An event that is over the “night” threshold will generate an immediate message.

A user may have multiple profiles associated with up to 15 different e-mail/pager/cell-phone addresses. For example, a user may have a profile for notifications of earthquakes anywhere in the world greater than magnitude 5.5, another profile for earthquakes in Japan greater than magnitude 4.5, and yet another profile for earthquakes in Alaska greater than magnitude 2.5 (probably not a good idea). For a given earthquake, if a user has overlapping thresholds, notifications are aggregated, and only one message will be sent per user address. Each individual profile can be deactivated and then reactivated as an alternate to deleting the profile. Automatic deactivation/reactivation of an account can be scheduled ahead of time using a pop-up calendar. This is useful if the user is going on vacation and wants to suspend notifications during that time.

There are currently about 50 predefined profile regions that users can choose from for notifications, and most users choose their own magnitude thresholds for one or more of these. Examples include 1) the conterminous United States, 2) California, 3) the New Madrid seismic zone, and 4) the globe. New regions can be added by the ENS administrator. However, users can also define their own profiles in several different ways: a rectangular profile region can be defined by inputting four latitude/longitude pairs, a circular profile region can be defined by inputting a center point and radius or by interactively picking the center point and radius on a map, or a custom polygon profile region can be defined by interactively picking points on a map or by uploading an XML file (for which the format is specified).

Any profile can be modified or deleted at any time by the user while he/she is logged in to his/her ENS account. In addition, any of the basic user information, including e-mail addresses, can be modified. A secure sockets layer (SSL) encrypts all user information passed over the Internet. Those who have indicated an affiliation of “scientist” or “network operator” will see two additional pieces of information associated with each profile. All the contributing regional networks will be listed, with the option to disable notifications that are a result of a solution from a particular network. In addition, the minimum and maximum depth of the event solution can be used to constrain notifications.


Previously, earthquake notifications were simply managed by a list server, but the capability to customize the notification for each individual user requires us to store each user’s options in a database. Each user sets up an “account” with his or her customization settings at the time he or she subscribes to the service.

The ENS main page has a link to extensive user documentation, and help (in the form of anchored links to this documentation) is provided for entering or choosing options in the registration form by clicking on any of the hyperlinked terms.

The initial registration page presents a form that collects all the information associated with the account: username, password, name, time zone, language, affiliation, aftershock exclusion choice, updates choice, and defer notifications at night choice. The user must enter a CAPTCHA code (a verification code that is an image on the registration page to prevent “bot” attacks, or software attacks that sign up for thousands of e-mail accounts in a short period of time and cause the server to fail) (CAPTCHA 2007). Clicking on the “Submit” button will then bring users to the next page where they enter the first e-mail address to which they want notifications to go. An opportunity to enter additional e-mail addresses, cell numbers, etc. is available after the initial setup is completed. There is a link to assist anyone who wants to have notifications sent to a cell phone but doesn’t know the e-mail address.

[Figure 1]

Figure 1. Example ENS user profile Web page. The profile shown is for a polygon of the continental United States with different day/ night magnitude thresholds. Messages go to both text message and e-mail accounts.

After the user submits the first e-mail address, an e-mail is automatically sent to that address containing a confirmation code. This code must be entered on the subsequent ENS Web page. The e-mail usually arrives within a few minutes, but users can exit the Web page and browser and return by logging in with a username/password anytime within six weeks of registration. The confirmation code can then be entered by choosing the “My Addresses: Register/Confirm Address” Web page link in the navigation area on the left side of the page. Once the confirmation code has been entered, the user may log out or choose to view, modify, or delete the two default profiles by choosing the “Return to Profiles” link on the bottom of the Web page or by choosing “My ENS Profiles” at the top of the navigation links on the left side of the page. When a new user account is established, the various options are all set to the default unless the user changes them (figure 1). Two default profiles are set up initially for each account: notifications for worldwide earthquakes of magnitude 5.5 and greater and notifications for U.S. earthquakes of magnitude 4.5 and greater. These profiles can be modified or deleted, and the user can define additional profiles. Users can make modifications to any settings or profiles associated with the account at any time by logging into ENS with usernames and passwords. The only piece of data that cannot be easily changed is the username because this is the primary key, and all the account settings are associated with that field in the database. However, a new username can be established by deleting the account and resubscribing, or it can be changed by the ENS administrator. Users who need assistance can send e-mail to ensadmin@usgs.gov, and they will usually receive a response within 24 hours. Support inquiries are tracked by a ticketing system that is cleared daily.

Figure 2 is an example of a notification for the same earthquake in the three formats that are offered: plain text e-mail, HTML-formatted e-mail, or cell/pager format. The e-mail messages contain basic information about the earthquake and hyperlinks to the event-specific Web page and to the contributing seismic networks

[Figure 2]

Figure 2. Example notifications in three formats: plain text e-mail, HTML-formatted e-mail, or cell/pager format. The content contains basic information about the earthquake, and the e-mail messages also include hyperlinks to the event-specific Web page for additional details and images.


The ENS relational database is made up of two databases and 15 tables in a MySQL database format. The Web pages use PHP to communicate with the database. The combination of PHP and MySQL is a powerful open-source standard for database Web applications (Williams and Lane 2004). The ENS notification process is run with Perl scripts (Wall et al. 2000) that query the database with SQL commands redundantly on five machines: one in the Pasadena, California, USGS office, one in the California Institute of Technology Seismology Lab computer room, and three in the Golden, Colorado, office. All five are running the Quake Data Distribution System/Quick Data Merge (QDDS/QDM) software (Jones and Oppenheimer 2004; Fee et al. 2007) in use under the Advanced National Seismic System (ANSS) for earthquake data exchange. As the Earthquake Information Delivery System (EIDS) becomes the standard at ANSS, we will switch ENS to EIDS as well (http://www.cisn.org/ahpeid/ahpeid_final.pdf).

Each of the five ENS machines receives earthquake events from QDDS and uses identical logic in its own version of QDM and the mail-input.pl Perl script to determine if the event should be processed (figure 3). If the event is determined to require processing (i.e., it is a new event or is a significant update to an existing event), an instance of mail-process.pl running on each machine then picks up the event, generates messages to send for the event, and places these messages in the local database on the machine. Finally, an instance of mail-send.pl running independently on each machine asks the primary database (on the primary machine) for a list of messages to mail out and then sends out these messages.

[Figure 3]

Figure 3. Flow chart depicting ENS processing. All five servers perform all functions, but the secondary servers use the queued notifications on the primary server. If the primary server fails, the list from any of the secondary servers can take over.

Because all the messages are generated on each machine, any secondary machine can take over as primary in the event that the original primary fails. Fail-over is currently a manual process that requires an ENS administrator to designate a new primary and then tell all the remaining secondary machines to use the new primary as the primary. Fail-over will ideally be an automated process; however, determining the difference between a true fail-over and a normal network glitch is a nontrivial task, because a glitch is simply a temporary drop-out in the network connectivity that usually lasts one to a few minutes and then is restored.

An extensive Web-based administration area allows the ENS administrator to monitor the system; provide user support; manage predefined regions, aftershock exclusion regions, and user priorities; view user statistics; and send messages to all users (figure 4).

[Figure 4]

Figure 4. ENS administrative Web page is the control center for all administrative tasks and ENS system information.


ENS supports a very wide range of user needs and demographics. Currently, there are more than 114,000 subscribers. They make up more than 200,000 user profiles, of which 3,600 are using customized notification areas. Figure 5 indicates the makeup by Internet domain, an indication of some useful aspects of distribution. For example, there are more than 1,000 users in the military (.mil) domain and 2,390 in the government (.gov) domain, but most users receive messages via private providers, and most of these are likely to be individual users.

We provide the most rapid notifications for more than 2,800 priority users as well as for more than 1,000 scientists. In a typical day about 188,000 messages go out, 50 new users sign up, and nearly 35 events are processed. These numbers increase dramatically immediately after significant earthquake sequences occur. For example, after the 2 April 2007 magnitude 8.1 Solomon Islands earthquake, ENS sent out 972,009 e-mails. With about 114,000 current subscriptions and four machines, this entire process takes up to 15 minutes. The bulk of the time is used for sending the e-mails; however, notifications to emergency responders are sent within the first minute or so of event determination.


ENS notifications are only as rapid and reliable as the seismic solutions generated by, and provided to, the ANSS and NEIC. We are continuing efforts to expedite earthquake information at NEIC for global events, within the ANSS for U.S. events, and with our international partners to automate and expand real-time coverage of the global events at lower magnitude thresholds and increased accuracy.

[Figure 5]

Figure 5. ENS users’ Internet domain distribution. The largest percentage of ENS accounts are in the public domain (.com, .net). Users from universities (.edu), emergency response agencies (.org, .us) and government agencies (.gov, .mil) are also represented.

The capacity to check individual users’ notification preferences allowed via database queries can be expanded. With the advent of new rapid earthquake information systems and products (e.g., Sipkin et al. 2006; Wald, Wald et al.,2006), it is natural to expand the capabilities of ENS to allow users to receive notifications triggered not just by magnitude and location, but also (or rather) based on the observed shaking intensity or even the likely impact of an earthquake.

With data from the “Did You Feel It?” (Wald, Quitoriano, Dengler, and Dewey, 1999) and ShakeMap (Wald, Quitoriano, Heaton et al., 1999) systems, notification could be based on the maximum intensity or acceleration determined within the profile region. Coupled with PAGER (Wald, Earle et al., 2006) capabilities, users will be able to set thresholds of population exposure to levels of intensity, and after further development, set thresholds for notification based on the likelihood of casualties or economic impact. Adding ShakeCast capabilities (Wald et al., 2007) to ENS would ultimately allow users to receive notifications of the likelihood of a specified ground-motion level at specific sites, with individual sites or facilities having assigned vulnerabilities and associated damage likelihoods.

Finally, we are using statistical analyses of the ENS Web page use (users’ paths through the Web pages and time spent on each page, etc.) to improve the user interface and experience of the registration process as well as the customization interface.


The current weaknesses of the system are the lack of an automatic failover mechanism and the fact that all user interactions have to go through one master database node. If the master database goes down, the system can still process events and send notifications, but users cannot access their accounts and profiles. Requirements to upgrade, harden, and grow the system in the future are being determined.

The earthquake information delivered through the ENS is preliminary. Subsequent review usually results in some revision to the data, and all users are advised to check the USGS EHP pages at http://earthquake.usgs.gov/ for updates. Data users are cautioned to consider carefully the provisional nature of the information before using it for decisions that concern personal or public safety or the conduct of business that involves substantial monetary or operational consequences. Earthquakes are a common occurrence, and many are either not large enough to cause damage or not located sufficiently close to population centers to produce damage. E-mail alerts sent through ENS do not imply an impending threat.

ENS is an informational tool and not a robust earthquake or tsunami warning system. The USGS does not produce tsunami warnings. For information about tsunamis, please refer to the information given on the NOAA Web site http://www.tsunami.noaa.gov/ . On a global basis, earthquakes of magnitude 5.0 or greater are generally reviewed and distributed by ENS within 20 minutes of their occurrence. Some events of magnitude 5.0 to 6.0 in remote parts of the world—especially on midocean ridges in parts of the Southern Hemisphere—may not be distributed until 24 hours after their occurrence. Smaller events in some parts of the world are not detected because of the lack of a dense network of instruments in that area. Within the United States, widely felt earthquakes are generally distributed within five minutes. Additionally, processing and sending the messages typically takes 30 minutes. The USGS cannot guarantee the receipt or timeliness of an e-mail after it has been sent.

ENS is an evolving system; facts and figures directly related to ENS contained herein were accurate at the time of this writing but are subject to change as ENS grows. We are always working to improve ENS



The following ANSS member agencies provide information directly to the ENS system:

Additional national and international cooperating agencies are listed on the Web page http://neic.usgs.gov/neis/bulletin/symbols.html 


Fee, J., D. Oppenheimer, and A. Jones (2007). QDM (Quake Data Merge) Java Real Time Merged Catalog Software Documentation, ftp:// ehzftp.wr.usgs.gov/QDM/QDM.html .

Jones, A., and D. Oppenheimer (2004). Quake Data Distribution System (QDDS), ftp://ehzftp.wr.usgs.gov/QDDS/QDDS.html .

Sipkin, S. A., J. R. Filson, H. M. Benz, D. J. Wald, and P. S. Earle (2006). The Advanced National Seismic System (ANSS) delivers improved earthquake data processing, information products, and notification procedures. EOS, Transactions, American Geophysical Union87 (36), 365–366.

Wald, D. J., P. S. Earle, K. Lin, V. Quitoriano, and B. Worden (2006). Challenges in Rapid Ground Motion Estimation for the Prompt Assessment of Global Urban Earthquakes. Bulletin of the Earthquake Research Institute, 81, 273-281.

Wald, David J, and K. Lin (2007). USGS ShakeCast–Automating, Simplifying, and Improving the Use of ShakeMap for Post-Earthquake Decision Making , U.S. Geological Survey Fact Sheet 2007-3086, 6 pages.

Wald, D. J., V. Quitoriano, L. Dengler, and J. W. Dewey (1999). Utilization of the Internet for Rapid Community Intensity Maps. Seismological Research Letters 70, 680–697.

Wald, D. J., V. Quitoriano, T. H. Heaton, H. Kanamori, C. W. Scrivner, and C. B. Worden (1999). TriNet “ShakeMaps”: Rapid Generation of Peak Ground Motion and Intensity Maps for Earthquakes in Southern California. Earthquake Spectra 15 (3), 537–556.

Wald, D. J., L. A. Wald, D. Oppenheimer, and W. Leith (2006). Earthquake Information Products and Tools from the Advanced National Seismic System (ANSS). USGS Fact Sheet 2006-3050.

Wall, L., T. Christiansen, and J. Orvant (2000). Programming Perl. 3rd ed. Beijing and Cambridge, MA: O’Reilly Media, Inc.

Williams, H. E., and D. Lane (2004). Web Database Applications with PHP and MySQL. 2nd ed. Sebastopol, CA: O’Reilly Media, Inc.

U.S. Geological Survey
DFC PO Box 25046 MS-966
Denver, Colorado 80225 USA
lisa [at] usgs.gov



Posted: 18 January 2008