# EARTHWORM PROJECT SUMMARY

January 15, 1998

## History and Motivation

The `EARTHWORM` project was started in 1993, mainly in response to a number of common needs identified by regional seismic networks: The automatic processing systems used by most regional networks were aging, and maintenance costs were growing; advances in seismic research required data from new, sophisticated sensors in order to provide viable research data; growing demands for immediate societal utility called for new and highly visible real-time products; and finally, shrinking funding meant that most individual networks could no longer support local system development efforts.

Most of the processing systems then in use had a number of drawbacks which made it difficult to enhance them to meet the new requirements: They were built on vendor-specific products, which tied them to high-price vendors, and deprived them of the benefits of the rapidly growing mass market. They tended to be tightly integrated, in the sense that functionally unrelated parts of the system shared a common resource, such as processor cycles, internal data paths, or peripheral devices. This resulted in systems that were difficult to modify, as changes to one function could cause malfunctions in an unrelated area.

The initial `EARTHWORM` effort had the specific mission of replacing the aging Rex Allen / Jim Ellis Real Time Pickers (RTPs) at Menlo Park. These devices had functioned well for decades and had become the mainstay of Menlo Park's ability to produce rapid event solutions. However, replacement parts were no longer available, and there was an urgent need to produce a replacement system in minimum time. This meant producing a system which could process over five hundred channels of data quickly and reliably.

In response to this, a delegation from Menlo Park was dispatched to present these problems to Carl Johnson, then at the University of Hawaii. Carl had produced many, if not most, of the seismic processing systems to date. The hope was that having been instrumental in creating the current situation, he might be in position to assist us in getting out of it. The visit bore fruit. Carl provided a number of ideas and algorithms that became the core of a new, common seismic processing system. As the system developed, a community of users and developers grew around it. The Council of National Seismic Systems formalized this process by a resolution creating a board of directors to guide its development. The effort currently consists of a that operate the system or it's derivatives and contribute to its development. Coordination of this effort is centered at the National Seismic Systems Project of the USGS in Golden, Colorado, which functions as the clearing house for development, distribution, documentation, and support.

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Design goals

One of Carl's most significant contributions is a set of principles to guide the design and implementation of a seismic processing system that would avoid some of the pitfalls of its predecessors:

- Modularity: each function performed by the system should be encapsulated into a module that can function independently of other modules, in terms of hardware as well as software. The implication is that a set of critical system functions can be guaranteed to be independent of other functions in the system. Thus, new, experimental functions can be added without disrupting pre-existing critical operations. Also, quality assurance can be performed on a module-by-module level, rather than for the entire system. This has proved to be a difficult principle to adhere to in practice. First, one has to resist the temptation to use intermediate results already computed by other modules, and second, to resist the lure of using various common utilities which would streamline operations.
- System independence: Such modules should operate on various brands of computer hardware and operating systems, and various types of such computers can be linked together to operate as one system. This, with the idea of modularity above, implies that the system can gradually migrate from one type of computer to another without disruption. In practice this means using only standardized portions of various computer systems, and isolating any unavoidable system- specific functions in standardized wrapper routines.
- Scalability: The system is to provide a smooth cost-performance curve to accommodate large as well as small networks. This was perhaps more significant prior to the availability of cheap, powerful mass-produced computers. However, it is still relevant in regard to license fees for included commercial software.
- Connectivity: The assumption is that such systems are no longer isolated, but have to interact quickly and reliably with other automatic real-time systems, interactive analysis systems, and various notification schemes. The objective is to provide connectivity at various levels of automatic and interactive processing, so that such systems can be configured to operate in configurations ranging from complete stand-alone operation to functioning as nodes in a distributed wide-area system.
- Robustness: Traditionally, the role of seismic processing systems was mainly one of research support. As a result, system reliability was naturally less important than cost, time to completion, and features. However, the new responsibilities to the press and emergency response agencies required very high levels of system reliability, especially during seismic crises, when input data and power may be interrupted, and system loads may increase dramatically. Thus issues like error detection and recovery, time-to-repair, graceful degradation, and load control were becoming vital, and had to be designed into the system. The costs of robustness are often not appreciated, in terms of time to design, implement, and test, as well as costs for suitable hardware and ancillary equipment.

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System Architecture:

Carl Johnson also provided a system architecture which implemented the above design goals. This basic scheme was developed by the `EARTHWORM` team at Menlo Park, and resulted in the scheme described below.

An `EARTHWORM` system consists of a set of modules 'immersed' in a message passing 'medium'. Each module performs some coherent task, such as data acquisition, phase picking, etc. Modules communicate by broadcasting and receiving various messages such as packets of trace data, phase picks, etc. The message passing scheme is analogous to radio communications: It consists of a message-carrying 'medium' and a set of standard routines which can be thought of as multi-frequency two-way radios operating in this medium. Modules can use these routines to broadcast messages into this medium on a specified 'frequency', and to 'tune in' to messages on specified 'frequencies'. Significant properties of this scheme are that: (1) a module cannot be prevented from broadcasting a message whenever it chooses; (2) any number of modules can listen in to some sending module(s) without affecting that module; (3) a module receives only the messages of interest to it and it is notified if it missed a message.

This 'medium' (the `EARTHWORM` transport layer) operates within one computer as well as between different computers. Standard TCP/IP network broadcasts (UDP) can be used to carry a batch of messages between computers, and shared memory regions are used to simulate such broadcasts within a computer. Each participating computer can be equipped with multiple network ports and multiple shared memory regions. Special adapter modules are used to link the message flows between a shared memory region and a network cable. Thus an `EARTHWORM` system can be configured to have a geometry of message passing paths tailored for a specific application, operating on any number of computers. Note that this scheme operates within one `EARTHWORM` system, spanning a maximum distance of several hundred meters. Message exchange between remote `EARTHWORM`s is handled by a different mechanism. The selective 'frequencies' of this 'medium' are implemented by attaching 'shipping tags' to all messages. They specify the module which created the message, the type of message it is, and the installation where the `EARTHWORM` system is running. Thus, for example, a message may be labeled as being a p-pick produced by the Rex Allen picker at Menlo Park, or a location produced by Hypo-inverse at Seattle. These tags are then used by the receiving routines to provide only the desired messages to a listening module.

The modules are independent main programs. Each module has free use of the file system and other system facilities. However, the `EARTHWORM` system offers several suites of support routines that can be used by the program to make it a compliant `EARTHWORM` module. One such suite is the collection of message passing routines (transport routines). These are used to acquire input data by requesting messages of certain type(s), and to broadcast output messages. Another set of routines is used to effect operating system independence by providing a common set of 'wrapper' routines for system-specific functions. For example, the system routines for starting a thread are different on Solaris and NT; the `EARTHWORM` system provides routines for both systems with the same name and arguments. Thus, if a program uses that routine, it can run on either operating system: the proper system-specific version of that routine will be automatically inserted when the program is built. This suite currently contains such 'wrappers' for all common functions. Routines are added as required. Moving `EARTHWORM` to a new operating system involves creating a new set of such 'wrapper' routines. `EARTHWORM` currently offers 'wrappers' for OS/2, Solaris, and Windows NT.

Modules generally read a configuration file at startup time. This file contains basic `EARTHWORM` parameters which define the module, specify which message 'medium' (message ring) it wishes to listen to, and which message ring it wishes to broadcast it's output messages to. In addition, this file can contain arbitrary operating parameters specific to its operation.

Error detection is accomplished via several mechanisms: Any module may broadcast an error message. Such messages are forwarded to a special module (StartStop, below), which takes appropriate actions based on the nature of the complaint. Each module can also provide a periodic heartbeat; if this heartbeat should cease an error would then be declared and processed. A module may also request to be restarted if its heartbeat should cease. In addition, the `EARTHWORM` as a whole can produce a heartbeat to an external monitoring device. Such a monitoring device, capable of generating pager messages, is available as part of the `EARTHWORM` system.

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Types of modules and functions:

The suite of modules available in the `EARTHWORM` system is quite varied, but can be classified into several categories:

- 1. System: Several modules are used to provide control over the system and error reporting:

- StartStop is a module, which starts and stops the `EARTHWORM` system. Like other modules, startstop reads it's configuration file, which contains the 'blue print' for the system. It specifies the message rings to be created, lists all modules to be started and the parameter files they are to read.
- StatusManager: It's role is to process error messages and heartbeats from individual modules. Each module can post a file containing specifications for how to process it's various error messages, such as what actions (email, pager, etc) to take based on the rate of recurrence.

2. Data Sources: These are modules that introduce data into an `EARTHWORM` system. These consist of three types:

- Data acquisition modules, (such as adsend) which perform real-time control of data acquisition hardware and produce streams of trace data messages;
- Data import modules, (such as coaxtoring, import_generic, import_scn, rcv) which connect to distant processing systems and receive various types of messages. These are then typically checked for validity, converted into locally known message types and broadcast into the local `EARTHWORM`.
- Data players(such as tankplayer), which can read historic data from archive files (such as trace data or phase picks) and broadcast them in the correct time order. These modules have been of critical value for analyzing rare malfunctions and quality assurance testing.

- 3. Processing Modules: These include the majority of the modules. They receive their input by listening for some specific type on a specified message medium, perform some seismic function, and produce occasional output messages. Examples include

- phase pickers (pick_ew) which listen to selected trace data, and broadcast phase messages, associators (binder_ew), which listen to phase picks and produce trial locations, etc. There are then follow-on modules for producing conventional hypocenters (hyp2000_mgr, eqverify, eqproc, eqcoda, eqbuf). A special subset of these modules are the 'trigger' modules. These process input data, such as trace or picks, and produce an event message, stating the type of event, the participating stations, and the time period of the event. Examples include hypocenters, low frequency, and STA/LTA coincidence.

- 4. Output Modules: These modules move data from an `EARTHWORM` system into post- processing systems of various types. Examples include:

- Export modules, which connect to distant systems and manage the long-distance sending of specified message types (export_generic, export_scn, vdl).
- Servers: These input standard `EARTHWORM` messages, such as trace data, store this data for some period of time, and offer access to this pool of data via a service on the internet (wave_serverV).
- Notification modules: These move data to external systems when a significant vent has been detected (eqalarm, pagerfeeder). This generally involves moving files of summary data to systems, which determine what notification actions should be taken.
- Post-processing interface modules: These modules listen for messages indicating that an event has been detected, go to various servers to obtain the requested trace data, format this data to suit various packages, and deliver the requisite files to a remote post-processing system. Examples include interactive seismic analysis packages, web page generators, and dBase's.

- 5. Record/Playback Modules: This is a set of modules which can create and play back segments of trace and pick data. The main use for this is for fault analysis and creation of test suites. See wave_serverV, tankplayer, and waveman2disk for creating and replaying trace data. Also see trig2K_putter getter.
  - The wave_serverV can be used to extract everything in an `EARTHWORM` ring to a circular buffer file for for special client programs to extract time periods into permanent files.
  - The data player, tankplayer can read historic data from archive files (such as trace data or phase picks) and broadcast them in the correct time order into an `EARTHWORM` ring.

  A table of module names organized by type of input, type of output and message type is useful to see how the different modules interact.

  Several example configurations of the modules and what they do are provided with details on what each module does relative to the others.

  The EARTHWORM development team is headed by Alex Bittenbinder and coordinated by Barbara Bogaert; both with the U.S. Geological Survey.