How one utility uses earthquake data for earthquake mitigation and rapid emergency response

How one utility uses earthquake data for earthquake mitigation and rapid emergency response

Marcia K. McLaren
Pacific Gas and Electric Company Geosciences Department
245 Market Street, Room 420, Mail Code N4C San Francisco, CA 94105

Abstract
The Pacific Gas and Electric Company takes a proactive role in preparing for and responding to California earthquakes. This role includes (1) the development of a GIS application that allows viewing, via the PG&E intranet, of earthquake data and PG&E facilities within moments after an earthquake and (2) installing over 50 strong motion instruments in critical buildings and substations within the greater San Francisco Bay Area and critical hydro dams. Earthquake data from the U. S. Geological Survey (locations, magnitudes, and ShakeMaps) are “pushed” to PG&E. Strong motion data from PG&E instruments are compared to the initial ShakeMaps, and added to subsequent ShakeMap revisions. By utilizing data products from the USGS, in addition to our own data, we are able to more effectively direct our emergency response efforts, assess damage, and restore gas and power to customers.

Introduction
The Pacific Gas and Eletric Company is proactive in its approach to preparing for and responding to California earthquakes. Using web-based GIS technology via the PG&E Intranet we have vastly improved our ability to disseminate earthquake information quickly and easily within PG&E. In this paper I describe 1.) our web-based tool, why we need this technology, how it works, and how we use it, and 2.) the PG&E Strong Motion Instrument Program, which was implemented for site specific damage assessment at critical PG&E facilities and to provide data to the U. S. Geological Survey’s (USGS) regional ShakeMaps.

Web-Based GIS Application
PG&E’s service territory covers nearly 2/3 of the state of California and includes several significant seismic sources, the largest being the San Andreas fault system. When an earthquake occurs we not only need to know where it occurred and how big it was, but more importantly, how close was it to a PG&E facility? We need to be able to assess potential damage or impact to our facilities and disseminate that information quickly to those that need to know.

Since 1996 the USGS has been posting current (the last 7 days) California earthquake data on their website (http://quake.wr.usgs.gov). These data include earthquake locations, magnitudes, and more recently, ground motion estimates from ShakeMaps. The earthquake locations are displayed on maps, with symbols sized by magnitude and color-coded by last hour, last day, and last week. ShakeMaps are displayed on a separate map. The earthquake locations generally are available within minutes after an event; ShakeMaps are available within about 10 minutes. ShakeMaps are generated for California earthquakes of magnitude 3.5 and greater.

PG&E has been using ESRI products for GIS since 1993 to maintain geocoded databases of their facilities (e.g. service centers, pipelines, substations, power plants and transmission lines). However, following an earthquake it was not easy to integrate the USGS earthquake information with our facility information for rapid decision making. Furthermore, we wanted to be able to display everything on one map. A solution to our problem presented itself in 1999 when we discovered the web-based GIS software tool called MapGuide, by Autodesk. Our application of MapGuide is nicknamed the MapServer. The software resides on a server and links to several PG&E databases (e. g. hydro dams, substations, gas lines) using the Intranet. The USGS “pushes“ earthquake data to PG&E using UDP packets through a secure port via the Internet. The earthquake data and PG&E facilities are available on the MapServer as layers. The earthquake locations are shown similar to the USGS web site, with symbols scaled to magnitude and color coded according to time. ShakeMaps are also imported and shown as a separate layer. We are currently downloading the ShakeMap files via the USGS website, however, in the near future we will have them automatically “pushed” to us via FTP.

Figure 1 shows how we use the MapServer. PG&E facilities and earthquake locations are shown on the map for the southern San Francisco Bay Area and represent a particular point in time. All of the available layers of information can be found by scrolling along the left side of the map. Layers are turned on or off simply by clicking a check in the box next to the layer name. Commonly used buttons above the map allow for zooming in or out, rescaling, selecting or printing. Dropdown menus above the buttons allow options such as viewing distances using point-click-drag distance measuring and links to other GIS (MapServer) applications that are specific to a particular group, such as to hydro or electric transmission. Our specialized Quake Tools menu includes an option to refresh the map to get the latest earthquake locations and an archive feature for plotting past earthquakes over designated magnitude and time ranges. This feature is particularly helpful for keeping track of seismicity patterns. With the MapServer we have been able to combine layers into one view for rapid assessments. Placing the cursor on any of the symbols on the map produces a flag of information; for example, time, date, location and magnitude information from a particular earthquake, peak ground motion values in units of g from a ShakeMap contour, or facility information from a building.

In Figure 1 we shows how we used the MapServer to compare the location of PG&E’s facilities with a magnitude 4.9 earthquake that occurred on 13 May 2002, near Gilroy, CA. We were able to see immediately how close the earthquake epicenter was to nearby 115 KV and 500 KV electric lines and, perhaps more importantly, that the earthquake did not occur beneath the lines or associated towers. Also shown are the peak ground motion contours from the ShakeMap. In this case the largest ground motion estimate (inner-most contour) was .2 g.

The MapServer is available to all of the various groups at PG&E, and all levels of management. Double-clicking on an earthquake symbol produces a separate page of information about the earthquake, including a list of all facilities within 50 miles of the earthquake. Fifty miles was chosen as the default radius because the California Department of Safety of Dams requires PG&E to walk-down any hydro facility within fifty miles of a magnitude 5 earthquake. The facilities are listed by distance from the event and alphabetically by facility type (e.g. dams, substations, buildings, etc.). This allows PG&E personnel quickly to see which facilities they need to look at first. The list can be printed out and immediately available to field crews or emergency response personnel.

PG&E Strong Motion Instrumentation Program
The second aspect of PG&E’s earthquake preparation is the installation of strong motion seismic instruments for direct site-specific damage assessments following a significant earthquake. These instruments are part of the PG&E Strong motion Instrumentation Program, consisting of 50+ strong motion accelerometers. The majority of the instruments are quasi-free field accelerometers, located in one-story cement slab critical buildings and substation control rooms. Five hydro dams are instrumented on the crest and abutments. The instruments are from various manufacturers and vintages, dating back to about 1991. All are trigger-only systems. Generally data are manually downloaded via phone lines; some of the instruments have the capability to, upon triggering, push a small ascii file of key information to a PG&E computer.

Both the manually downloaded and automatic data are used to assess facility performance following an earthquake. This assessment includes comparing the recorded data to the building design specifications. Such information can be used to decide whether or not a building is safe to re-occupy. The strong motion data from PG&E instruments are also compared to the initial ShakeMaps, and added to subsequent ShakeMap revisions. A future enhancement of the MapServer will be to link these ground motion data to the MapServer, so that the values will show as labels when the cursor is placed over the instrument locations.

Conclusions
Our goal has been to find the most efficient and secure way to integrate as much information as is available, via the Internet and Intranet after a significant earthquake. Our web-based GIS tool and strong ground motion instruments at critical facilities provides us means to achieve this goal. By utilizing data products from the USGS, in addition to our own data, we have been able to more effectively direct our emergency response efforts, assess damage, and restore gas and power to customers.

Figure 1. A sample view of the PG&E MapServer. Shown are earthquake locations (yellow or blue colored squares and diamonds), ShakeMap peak ground motion contours (yellow), transmission lines (see legend in figure) and critical buildings (stars and checkered circles). The large blue triangle is the Magnitude 4.9 earthquake of 13 May 2002. Green and black checkered circles are locations of PG&Eowned strong motion instruments at critical facilities.