Chapter 4. Viewing Results

Currently, the Scream software does not allow display of strong motion or unified status packets.

4.1 The Unified Status Packet

The unified status packet is a special, binary coded status message from the digitiser that is transmitted every second. It allows a connected system to determine the reliability of strong motion data, and is intended for realtime monitoring and alarm systems.

Some example packets are shown below. The first packet is from a system that does not have a GPS lock, and thus has no reliable time source.

00000000032A6C1F | LW-B808/ttyS2/rhod | 2008-03-12T12:42:43.000Z | LW -B80801 | unknown | unified status | 19 words

| Clock status: locked=0, differential=-2147483647us, source=GPS receiver, last_locked=1989-11-17T00:00:00.000

| Unable to interpret GPS receiver status.

| Channel 'Z' (instrument 0) flags:

| Channel 'N' (instrument 0) flags:

| Channel 'E' (instrument 0) flags:

This packet is from a system with a reliable time source:

000000000024557C | LW-A830/Port A/loc | 2008-03-12T12:43:17.000Z | LW -A83001 | unknown | unified status | 27 words

| Clock status: locked=1, differential=-694us, source=GPS receiver, last_locked=2008-03-12T12:43:17.000

| GPS receiver status: fix=3D, latitude=+51.216703deg, longitude=-001.098548deg, elevation=+000105.000m

| Channel 'Z' (instrument 0) flags:

| Channel 'N' (instrument 0) flags:

| Channel 'E' (instrument 0) flags:

| Channel 'X' (instrument 0) flags:

| Channel 'Z' (instrument 1) flags:

| Channel 'N' (instrument 1) flags:

| Channel 'E' (instrument 1) flags:

Channel flags may occasionally be observed. These indicate that the data is not reliable for some reason. Typically these are observed immediately after a time step when the digitiser's clock is synchronised for the first time. This will correspond to a spike in the waveforms as the FIR filters charge.

4.2 Example Strong Motion Packet

The strong motion packet contains calculated strong motion data in floating point format in ASCII. The data are in ground units (gal, kine, etc.).

A typical strong motion block looks like this:

0000000000245B5B | LW-A830/Port A/loc | 2008-03-12T12:47:58.000Z | LW -A830SM | unknown | strong motion | 50 words

| Windowed MMA | 0Z | -4.09785 -4.09660 -4.10911

| Windowed MMA | 0N | -4.19176 -4.18925 -4.19427

| Windowed MMA | 0E | -4.43434 -4.43434 -4.44563

| Windowed MMA | 0h | 6.10199 6.10026 6.11192

| Windowed MMA | 0a | 7.35028 7.34815 7.36480

| PGA | 0Z | 0.0125049

| PGA | 0N | 0.00502158

| PGA | 0E | 0.0112897

| PGA | 0h | 0.0123561

| PGA | 0a | 0.0175797

| RMS | 0Z | 0.0113237

| RMS | 0N | 0.00376618

| RMS | 0E | 0.0125441

| RMS | 0h | 0.0130973

| RMS | 0a | 0.0173137

| SI | 0Z | 0.615240

| SI | 0N | 0.628953

| SI | 0E | 0.663583

| SI | 0h | 0.914289

| SI | 0a | 1.10202

The format of this packet is described fully in document SWA-RFC-STMN.

4.3 Viewing Packets

On an EAM or NAM that is connected to a strong motion data source, the strong motion packets will be decomposed into thirty individual streams per instrument. These will then be available for any recording, conversion and/or transmission function, the same as any other stream.

The thirty additional streams produced when in strong motion mode are shown in the following table, where 𝕊 represents the System ID and ℤ identifies the component ('Z' for vertical, 'N' for North/South or 'E' for East/West).

4.4 The STA-DISP Strong-motion Display Unit

As part of a seismic hazard monitoring system, a real-time display unit (the CMG-STA-DISP) has been developed. This displays the peak ground acceleration and spectral intensity values being recorded by an instrument.

The CMG-STA-DISP has several options for warning and alert levels, peak hold etc. Alarms can be raised via relays or SCADA current outputs. The unit is further described in the document MAN-SMD-0001.